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Department of Immunology, Mayo Clinic and Mayo Foundation, Rochester, MN 55905
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Secretory IgA (S-IgA)3 is the
main Ab secreted by the mucosa of the airways, gastrointestinal tract,
and other mucosal tissues (reviewed in 8 . A high proportion of
Ig-producing cells in the mucosal lymphoid tissue is committed to the
IgA isotype, and the majority of IgA in mucosa is derived from local
synthesis (9). Receptors for the Fc portion of IgA (Fc
R) have been
established on a variety of cell types, including lymphocytes (10, 11),
monocytes/macrophages (12, 13), neutrophils (14, 15), and eosinophils
(16). The importance of IgA in mucosal immunity is further supported by
the presence of secretory component (SC) in S-IgA (17). Epithelial
cells express the polymeric Ig receptor, which binds and mediates the
transepithelial transport of IgA from the basolateral side of the cells
into the lumen (8, 18). The SC is a soluble proteolytic cleavage
fragment of the extracellular domain of membrane-bound polymeric Ig
receptor (19). Addition of SC to IgA confers increased stability on the
resultant S-IgA by helping to hold the IgA monomers together (20) and
by masking proteolytic sites from proteases present in mucosal
secretions (21); however, the effect of the addition of SC on the
biologic activity of IgA is unknown. Recent studies showed that SC did
not modify the ability of IgA to mediate hemagglutination inhibition
and to neutralize influenza virus in vitro (22).
The SC consists of five Ig-like domains (23); this structure is used commonly as a cell surface receptor and an adhesion molecule. Furthermore, S-IgA immobilized onto Sepharose 4B beads potently stimulates eosinophil degranulation (24). These observations lead us to hypothesize that SC directly interacts with human eosinophils and plays an important role in activation of this leukocyte. In this report, we demonstrate a unique function of SC as a costimulatory molecule for effector functions of human eosinophils. This interaction between SC and eosinophils may provide a novel mechanism to regulate the magnitude of mucosal tissue inflammation.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Human S-IgA was obtained from Organon Teknika-Cappel (Malvern,
PA) or Accurate Chemical & Scientific (Westbury, NY). Purified human
serum IgA and IgG were purchased from ICN Pharmaceuticals (Costa Mesa,
CA). Purified human SC was kindly provided by Dr. Michael W. Russell
(University of Alabama, Birmingham, AL) (25). The IgG fraction of goat
anti-human SC Ab and phycoerythrin (PE)-conjugated
F(ab')2 fragments of donkey anti-goat IgG Ab were
purchased from INCSTAR (Stillwater, MN) and Jackson Immunoresearch
Laboratories (West Grove, PA), respectively. mAb against human FcR
(My43, mouse IgM) and control mAb (anti-ox erythrocytes, mouse IgM)
were generously provided by Dr. Li Shen (Dartmouth Medical School,
Hanover, NH) (13). Mouse anti-human CD18 mAb (mouse IgG1) and
purified mouse IgG1, as a control, were purchased from Becton Dickinson
(San Jose, CA) and ICN Pharmaceuticals, respectively. Recombinant human
granulocyte-macrophage (GM)-CSF was purchased from Genzyme (Cambridge,
MA). Recombinant human IL-5 was generously provided by Schering-Plough.
Human serum albumin (HSA) and defined calf serum (DCS) were from Sigma
Chemical (St. Louis, MO) and HyClone Laboratories (Logan, UT),
respectively. Human neutrophil elastase and elastase substrate
(MeOSuc-Ala-Ala-Pro-Val-pNA) were purchased from
Calbiochem-Novabiochem (La Jolla, CA).
Cell preparation
Eosinophils were purified from peripheral blood obtained from normal volunteers as described previously (26). The percentage of eosinophils in peripheral blood leukocytes of these donors was <5%. Briefly, heparinized venous blood was layered onto 1.085 g/ml Percoll (made in PIPES buffer (25 mM PIPES, 50 mM NaCl, 5 mM KCl, 25 mM NaOH, 5.4 mM glucose, pH 7.4)) and centrifuged at 2000 rpm in Beckman CS-6KR (Beckman Instruments, Fullerton, CA) for 30 min. Plasma, mononuclear cells, and Percoll layers were removed, and erythrocytes were lysed by osmotic shock. The remaining eosinophil/neutrophil pellet was mixed with anti-CD16-bound immunomagnetic beads (Miltenyi Biotec, Sunnyvale, CA) and incubated for 1 h. The cells were then separated using a magnetic cell separation system (MACS; Miltenyi Biotec). The eluate was collected, and cell number and eosinophil purity were determined. Neutrophils were isolated using a gradient material, 1-Step Polymorphs (Accurate Chemical & Scientific), following the procedure recommended by the manufacturer. The purities of eosinophil and neutrophil preparations were >97%. All the isolation procedures were performed at 4°C or on ice.
Preparation of stimuli
Human S-IgA, serum IgA, and SC immobilized onto cyanogen bromide-activated Sepharose 4B beads (Sigma) or tissue culture plates were used as stimuli for eosinophils and neutrophils. Sepharose 4B beads were coupled to S-IgA or serum IgA, at a concentration of 5 mg protein/ml of packed beads, as previously described (24). To immobilize Ig or SC to tissue culture plates, 96-well flat-bottom tissue culture plates (Costar, Cambridge, MA) were coated with 50 µl of indicated concentrations of S-IgA, serum IgA, or SC diluted in PBS (pH 7.4) overnight at 4°C. Plates were then blocked with 100 µl of DCS or 2.5% HSA diluted in PBS for 2 h at 37°C. After blocking, the wells were washed twice with 200 µl of PBS before use. In some experiments, the wells were coated with 50 µl of 0.5 µg/ml human serum IgG overnight at 4°C before being subsequently coated with 50 µl of SC or HSA (as a control) diluted at 10 µg/ml in PBS for 2 h at 37°C. These plates were blocked with 100 µl of 2.5% HSA and washed twice with 200 µl of PBS before use.
Degranulation assay
Degranulation of eosinophils and neutrophils was induced by Ig immobilized onto Sepharose 4B beads as described previously with minor modifications (24). Briefly, 96-well round-bottom tissue culture plates (Costar No. 3799) were blocked with 50 µl of 2.5% HSA in PBS (pH 7.4) at 37°C for 2 h. After incubation, the wells were washed three times with PBS. Cells were washed once with RPMI 1640 medium containing 25 mM HEPES and 0.1% HSA and resuspended in the same medium at 5 x 105 cells/ml. Aliquots (100 µl) of cell suspension were added to the tissue culture plates. Cellular degranulation was initiated by adding 100 µl of Sepharose 4B beads coated with S-IgA or serum IgA (bead-cell ratio, 1:20). After incubation for 4 h at 37°C in a 5% CO2 atmosphere, cell-free supernatants were collected and kept at -20°C until assayed. To quantify eosinophil degranulation, the concentration of an eosinophil granule protein, eosinophil-derived neurotoxin (EDN), in the sample supernatants was measured by double Ab competition assay using radioiodinated EDN, rabbit anti-EDN Ab, and burro anti-rabbit IgG, as previously reported (27). Total cellular EDN was measured in supernatants from cells lysed with 0.5% Nonidet P-40 detergent. To quantify neutrophil degranulation, the concentration of elastase in the sample supernatants was measured by colorimetric assay (28, 29). Twenty microliters of samples or serial dilutions of elastase standards were mixed with 130 µl of HBSS with 10 mM HEPES in 96-well culture plates, and 50 µl of 2.5 mM elastase substrate (MeOSuc-Ala-Ala-Pro-Val-pNA) (30) was added. Reaction mixtures were incubated at 37°C for 1 h. After incubation, the absorbance at 405 nm in each well was measured with a microplate reader (Thermomax; Molecular Devices), and the elastase concentration was calculated using an elastase standard curve made in the same assay. Total cellular elastase was measured in supernatants from cells lysed with 0.5% Nonidet P-40 detergent. All experiments were performed in duplicate.
Superoxide anion generation
Generation of superoxide by eosinophils and neutrophils was
measured by superoxide dismutase-inhibitable reduction of
cytochrome c, as previously reported (31, 32). Flat-bottom
96-well tissue culture plates (Costar) were blocked with 2.5% HSA.
Freshly isolated eosinophils or neutrophils were suspended in HBSS with
10 mM HEPES, 0.1% HSA, and 100 µM cytochrome c (Sigma) at
5 x 105 cells/ml. Cell suspension (100 µl) was
added to the wells and stimulated with 100 µl of Ig-coated Sepharose
4B beads suspended in HBSS with 10 mM HEPES and 0.1% HSA (bead-cell
ratio, 1:10). In some experiments, Ig or SC immobilized onto tissue
culture plates were used as stimuli instead of Ig-coated Sepharose 4B
beads. In these experiments, 100 µl of cell suspensions and 100 µl
of HBSS with 10 mM HEPES and 0.1% HSA were added to the wells
precoated with Ig or SC. IL-5 (1 ng/ml) or GM-CSF (0.1 ng/ml) was added
to the wells to examine the effects of cytokines on eosinophil
superoxide production stimulated with immobilized SC. When the effects
of mAb to FcR and CD18 were tested, eosinophils were pretreated with
1/40 dilutions of anti-FcR mAb (My43) or control Ab, 10 µg/ml
anti-CD18 mAb, or 10 µg/ml mouse IgG1 for 15 min at room
temperature before the addition of Ig-coated Sepharose 4B beads.
Immediately after the addition of the cells and stimulus, the
absorbance at 550 nm in each well was measured with a microplate reader
(Thermomax; Molecular Devices, Menlo Park, CA), followed by repeated
readings for 3 h. Between absorbance measurements, the plate was
incubated at 37°C. Superoxide anion generation was calculated with an
extinction coefficient of 21.1 x 103
cm-1 M-1 for reduced cytochrome c
at 550 nm and was expressed as nanomoles of cytochrome c
reduction per 1 x 105 cells.
Flow cytometry analysis of SC binding
Binding of SC to eosinophils and neutrophils was examined by flow cytometry. Purified eosinophils or neutrophils (1 x 106 cells) were suspended in RPMI 1640 medium supplemented with 25 mM HEPES, 1% BSA, and 0.1% NaN3, and incubated with or without 30 µg/ml SC for 90 min on ice. Cells were washed twice with PAB buffer (PBS containing 0.1% NaN3 and 0.5% BSA, pH 7.4), and stained with 20 µg/ml goat IgG anti-human SC Ab for 30 min on ice, followed by 5 µg/ml PE-conjugated F(ab')2 fragment of donkey anti-goat IgG for 30 min on ice. The cells were then washed with PAB buffer and fixed with 1% paraformaldehyde in PBS (pH 7.4). The fluorescence intensity of individual cells was measured with a FACScan (Becton Dickinson, Mountain View, CA), and analyzed by Becton Dickinson lysis II software.
Binding of 125I-labeled SC
SC was radioiodinated by IODO-GEN Iodination Reagent (Pierce, Rockford, IL) according to the procedure recommended by the manufacturer. SC (63 µg) was labeled with 500 µCi of 125I, and the specific activity of labeled protein was 605 Ci/mmol. The binding of 125I-labeled SC to eosinophils was measured according to a method described previously for cytokines with minor modifications (33). Eosinophils (7 x 105 cells/sample) suspended in 50 µl of binding medium (RPMI 1640 medium supplemented with 25 mM HEPES, 1% BSA, and 0.1% NaN3, pH 7.4) were incubated with 50 µl of 12.5 nM 125I-labeled SC in the presence or absence of a serial dilution of unlabeled SC, S-IgA, or IgA for 2 h on a rotating table at 4°C. Cells were then overlayered onto 200 µl of DCS and centrifuged at 3000 rpm for 3 min. Pellets were frozen on dry ice and cut away from the supernatant. Radioactivity in the pellets was measured in a gamma counter (Packard, Downers Grove, IL).
Statistical analysis
All results are shown as mean ± SEM from the numbers of experiments indicated. The statistical significance of the differences was assessed with Student’s paired t test.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Previous studies suggested that both neutrophils (13, 14, 15) as well
as eosinophils (16) possess FcR. Therefore, we examined whether
S-IgA and serum IgA induce effector functions of these two cell types.
Purified eosinophils and neutrophils were stimulated with Sepharose 4B
beads coated with S-IgA or serum IgA, and degranulation was assessed by
measuring the amounts of EDN (for eosinophils) and elastase (for
neutrophils) in the supernatants. As shown in Figure 1
, serum IgA-beads induced both EDN
release from eosinophils and elastase release from neutrophils,
consistent with the expression of FcR on these two cell types
(13, 14, 15, 16). S-IgA-beads released approximately twice the amount of EDN
compared with those stimulated with serum IgA-beads
(p < 0.001). In contrast, there were no
significant differences in elastase released from neutrophils
stimulated with S-IgA-beads and serum IgA-beads. Thus, S-IgA is likely
a more potent secretagogue than serum IgA for eosinophils but not for
neutrophils.
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, left, both S-IgA and serum
IgA induced superoxide production from eosinophils in a
concentration-dependent manner. The stimulatory effects of these Ig
reached a plateau at 3 or 10 µg/ml. Striking differences were found
in the amounts of superoxide released; S-IgA induced significantly
larger amounts of superoxide production than serum IgA at the optimal
concentrations (p < 0.05). At 10 µg/ml,
eosinophils stimulated with S-IgA produced 
2.5-fold more superoxide
compared with those stimulated with serum IgA. In neutrophils, both
S-IgA and serum IgA induced superoxide production in a
concentration-dependent manner; however, there was no difference
between the magnitudes of neutrophil responses to S-IgA and to serum
IgA at the optimal concentrations (Fig. 2, right). S-IgA
induced less superoxide production than serum IgA at the suboptimal
concentrations (p < 0.05 at 1 µg/ml).
Altogether, these findings suggest that S-IgA stimulates eosinophil
functions more potently than serum IgA. In contrast, S-IgA
stimulates neutrophil functions similarly to or less potently than
serum IgA.
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The presence of SC in S-IgA, but not in serum IgA, is notable
(reviewed in 8 . Therefore, we hypothesized that SC binds to
eosinophils and activates their effector functions. To test this
hypothesis, we first examined whether eosinophils are able to bind to
SC by flow cytometry. Purified eosinophils were incubated with or
without SC, and SC bound to the cells was detected by anti-SC Ab
followed by fluorochrome-conjugated secondary Ab. As shown in Figure 3, in the absence of SC, minimal amounts
of SC were detected on the surface of eosinophils. In the presence of
SC, the binding was greatly increased, suggesting eosinophils do bind
to SC. The geometric mean fluorescence intensity of samples stained
with control Ab, anti-SC Ab (without SC), and anti-SC Ab (with
SC) were 77.2 ± 9.2, 76.7 ± 9.3, and 116.2 ± 13.0,
respectively (mean ± SEM, n = 3,
p < 0.01 between "without SC" and "with
SC").
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, when eosinophils were incubated with
12.5 nM 125I-labeled SC, substantial amounts of bound SC
were detected. This binding of 125I-labeled SC was
inhibited by unlabeled SC in a concentration-dependent manner,
indicating specific binding of SC to eosinophils. Furthermore, the
binding of 125I-labeled SC was also inhibited by unlabeled
S-IgA in a concentration-dependent manner albeit not as potently as
unlabeled SC. In contrast, binding of 125I-labeled SC was
not inhibited by unlabeled serum IgA.
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GM-CSF activates effector functions of both eosinophils (34, 35)
and neutrophils (36). Furthermore, IL-5 enhances various functions of
eosinophils, such as degranulation, helminthotoxicity, and survival,
and it is implicated in the pathophysiology of allergic diseases
(reviewed in 37 . GM-CSF and IL-5 can also induce superoxide
production from eosinophils (38). Thus, we examined whether binding of
SC to eosinophils leads to enhancement of their effector functions when
stimulated with these cytokines. Eosinophils and neutrophils, as a
control, were added to wells coated with SC in the presence or absence
of cytokines; superoxide production was measured. As shown in Figure 5A, left,
immobilized SC by itself did not induce eosinophil superoxide
production up to 120 min; GM-CSF, 0.1 ng/ml, by itself induced moderate
superoxide production; SC and GM-CSF worked synergistically and induced
considerable superoxide production. In contrast, as shown in Figure 5A, right, GM-CSF induced minimal superoxide
production from neutrophils, and immobilized SC did not enhance
superoxide production. Figure 5B summarizes five experiments
with a similar experimental design. Although immobilized SC by itself
did not induce superoxide production from eosinophils, immobilized SC
strikingly enhanced the eosinophil response to GM-CSF by 80% (mean of
five experiments, p < 0.01). Likewise, eosinophil
superoxide production stimulated with 1 ng/ml IL-5 was enhanced by
immobilized SC by 92% (mean of five experiments, p <
0.01). In contrast, immobilized SC did not affect neutrophil superoxide
production either in the presence or absence of GM-CSF.
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, this concept was
further tested by coimmobilizing SC and IgG onto the wells of tissue
culture plates. By itself, immobilized IgG induced superoxide
production from both eosinophils and neutrophils. Eosinophil superoxide
production stimulated with IgG was enhanced strikingly by SC
coimmobilized to the wells (107 ± 18% of enhancement, mean
± SEM, n = 3). In contrast, neutrophil superoxide
production stimulated with IgG was not enhanced by coimmobilized SC.
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Recent studies suggest that adhesion molecules, especially
ß2 integrins, play critical roles in eosinophil functions
stimulated by cytokines and lipid mediators (31, 32). Furthermore,
degranulation of eosinophils stimulated with immobilized IgG has been
completely inhibited by either mAb against Fc
RII receptors (32) or
mAb against CD18 (39), suggesting that IgG-mediated eosinophil
functions are controlled by both the Fc receptor and
ß2 integrin. Therefore, to investigate the mechanism of
SC on eosinophils, we examined the roles of the IgA receptor, FcR,
and ß2 integrin in eosinophil function stimulated with
serum IgA and S-IgA. An anti-FcR mAb, My43, inhibits binding of
IgA to neutrophils (13). As shown in Figure 7A, eosinophil superoxide
production stimulated with serum IgA was significantly inhibited by
this anti-FcR mAb (p < 0.05),
suggesting that FcR similar to that on neutrophils is involved in
eosinophil activation stimulated with serum IgA. In contrast,
anti-CD18 mAb did not show any effect on eosinophil superoxide
production stimulated with serum IgA. As shown in Figure 7B,
when eosinophils were stimulated with S-IgA, anti-FcR mAb
inhibited superoxide production minimally but significantly
(p < 0.05); in contrast, S-IgA-induced
superoxide production was almost abolished by anti-CD18 mAb, which
blocked the ß2 integrin (p <
0.01). Thus, the major difference in eosinophil function stimulated
with serum IgA and S-IgA is the involvement of ß2
integrin; SC is likely the critical molecule in this difference.
Consistent with this observation, as shown in Figure 8, eosinophil superoxide production
stimulated by immobilized SC and GM-CSF was completely inhibited by
anti-CD18 mAb.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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and 2), and an anti-FcR inhibits the eosinophil response (Fig. 7).
These results are consistent with previous observations showing that
both eosinophils and neutrophils express FcR (13, 14, 15, 16), bind IgA (14, 24, 40, 41), and can be stimulated through this receptor (14, 24, 42).
However, eosinophil and neutrophil responses to S-IgA were strikingly
different. In eosinophils, S-IgA induced more EDN release and
superoxide production than serum IgA; but in neutrophils, S-IgA and
serum IgA induced similar elastase release and S-IgA induced slightly
less superoxide production than serum IgA. Compatible observations by
others demonstrated that the eosinophil chemotactic response to IL-8
was enhanced by immobilized S-IgA but not by serum IgA (43).
Furthermore, Staphylococcus aureus opsonized with serum IgA
and S-IgA induced similar degrees of respiratory burst in neutrophils
(42). Therefore, it is apparent that S-IgA stimulates functions of
eosinophils more potently than serum IgA, and that S-IgA and serum IgA
stimulate functions of neutrophils similarly.
This stronger stimulatory effect of S-IgA compared with serum IgA on
eosinophils is unlikely due to the difference in binding efficiency of
S-IgA and IgA to solid surfaces, such as Sepharose 4B beads or plastic
plates, because the responses of neutrophils to immobilized S-IgA were
similar to or slightly less than those to serum IgA (Figs. 1 and 2).
The differences in the potencies of S-IgA and serum IgA cannot be
explained by the differences in IgA isotypes, because eosinophils
respond similarly to IgA1 and IgA2 (24). Thus, SC, which is bound to
S-IgA but not to serum IgA, may activate eosinophil functions. In fact,
we found that binding of purified SC to eosinophils was inhibited by
S-IgA but not by serum IgA (Fig. 4). SC immobilized onto the tissue
culture plates strikingly enhanced eosinophil superoxide production
stimulated with cytokines, such as GM-CSF and IL-5 (Fig. 5), or IgG
(Fig. 6); SC did not affect neutrophil superoxide production stimulated
with GM-CSF or IgG. We also noted that SC by itself does not provoke
eosinophil functions in the absence of other agonists. These findings
suggest that, in eosinophils, SC acts synergistically with other
agonists, such as cytokine and Ig, and stimulates their effector
functions. In contrast, neutrophil function is not affected by SC even
in the presence of other agonists. Thus, SC likely has a unique
capacity to stimulate eosinophils specifically.
Then, how does SC activate eosinophil functions? Our previous studies
suggest that adhesion molecules, especially ß2 integrins,
play crucial roles in eosinophil activation stimulated with cytokines
or IgG (31, 32). Eosinophil superoxide production stimulated with these
agonists was strikingly enhanced when cells were able to adhere to
substrates through the ß2 integrins (31, 32). In this
study, we found that ß2 integrins were involved in
eosinophil superoxide production after stimulation with S-IgA (Fig. 7B) but not with serum IgA (Fig. 7A).
Furthermore, eosinophil superoxide production on SC-coated plates was
also totally dependent on ß2 integrins (Fig. 8).
Therefore, ß2 integrins play critical roles in
up-regulation of eosinophil function by SC.
The remaining question is how SC stimulates eosinophil functions
through ß2 integrins. Although this issue is currently
under study in our laboratory, we can discuss several possibilities. It
is commonly accepted that integrins in a resting cell do not bind or
bind weakly to their ligands and that cellular activation is required
for firm interaction between integrins and their ligands (reviewed in
44 . Furthermore, ß2 integrins are often
promiscuous, binding to various molecules (45). Therefore, the first
possibility is that binding of SC may specifically stimulate the
avidity of eosinophil ß2 integrins. The second and more
likely possibility is that SC may serve as a ligand for
ß2 integrins. In fact, SC stimulated eosinophil function
only when eosinophils were stimulated with cytokines or Ig; this
characteristic is similar to stimulus-dependent up-regulation of the
ligand-binding capacity of integrins (44). Our Scatchard plot analysis
also showed that the binding of 125I-labeled SC to resting
eosinophils was largely of low affinity
(KD > 100 nM, data not shown).
Furthermore, SC belongs to the Ig supergene family (23, 46), a
structure shared by various ligands for integrins, such as ICAM-1 and
VCAM-1. The results of our preliminary experiments to identify the
receptor(s) for SC using Abs against known -chains of
ß2 integrins, including CD11a, CD11b, and CD11c, have
been inconclusive (data not shown). It is also possible that SC may
bind to another newly discovered member of ß2 integrins,
dß2, or to an as yet unidentified
member(s) of ß2 integrins on eosinophils. Alternatively,
SC may bind to different site(s) other than ß2 integrins
on eosinophils. In fact, Lamkhioued et al. (47) detected a 15-kDa
SC-binding protein in eosinophils by immunoprecipitation and
immunosorbent chromatography. While its identity is unknown as yet,
this molecule is clearly another candidate.
Although the receptors for SC are not yet identified, our study clearly indicates that SC enhances the effector functions of eosinophils, but not those of neutrophils. Therefore, SC and S-IgA may play important roles in regulating eosinophil functions in vivo in diseases associated with mucosal eosinophilia and in various allergic diseases. Interestingly, allergen-specific S-IgA is increased in sputa and nasal washing fluids from patients with asthma and ragweed hay fever, respectively (48, 49). Marked deposition of SC and S-IgA is found in skin tissues from patients with chronic eczema and atopic dermatitis (50). In addition, the presence of allergen-specific S-IgA in sputa, but not of specific IgA in sera, was associated with asthma symptoms (48). The concentrations of released eosinophil granule protein in sputa or bronchoalveolar lavage fluids correlated with the levels of S-IgA in patients with bronchial asthma (51) and chronic eosinophilic pneumonitis (52), suggesting that S-IgA may in fact induce eosinophil degranulation in respiratory mucosa in vivo. Furthermore, S-IgA induces not only degranulation and superoxide, but also other effector functions of eosinophils, such as parasite killing (53), production of lipid mediators (e.g., platelet-activating factor) (54), and synthesis of cytokines (e.g., IL-4 and IL-10) (55). Thus, circumstantial evidence suggests an association between S-IgA and eosinophil activation in diseases. Therefore, further studies on the interaction among SC, S-IgA, and eosinophils may lead to a better understanding of the mechanisms of various mucosal and allergic diseases. Finally, IgA has recently been recognized as a unique Ig among the various isotypes because of its restricted ability to use ancillary effector mechanisms, such as activation of complement, phagocytosis, and binding to effector cells (reviewed in 56 . It would be interesting to know how eosinophils interacting strongly with S-IgA may fit into this global paradigm of IgA and mucosal immunology.
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Acknowledgments |
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R mAb,
respectively. We also thank Dr. G. J. Gleich for critical reading
of the manuscript, Linda H. Arneson for secretarial
assistance, and Cheryl Adolphson for editorial assistance. |
Footnotes |
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2 Address correspondence and reprint requests to Dr. Hirohito Kita, Department of Immunology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905. E-mail address:
3 Abbreviations used in this paper: S-IgA, secretory IgA; FcR, receptor for the Fc portion of IgA; DCS, defined calf serum; EDN, eosinophil-derived neurotoxin; GM, granulocyte-macrophage; HSA, human serum albumin; PE, phycoerythrin; SC, secretory component.
Received for publication April 6, 1998. Accepted for publication June 17, 1998.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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receptor in humans. J. Exp. Med. 171:597. RII induce eosinophil degranulation. J. Clin. Invest. 95:2813.
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 M. A. Giembycz and M. A. Lindsay Pharmacology of the Eosinophil Pharmacol. Rev., June 1, 1999; 51(2): 213 - 340. [Abstract] [Full Text] [PDF]
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), Sepharose 4B beads coated with S-IgA (
) or serum IgA
(
) for 4 h. Eosinophil degranulation was quantified by
measuring the concentration of EDN in the cell-free supernatant by RIA.
Neutrophil degranulation was quantified by measuring the concentration
of elastase in the cell-free supernatant by enzymatic assay. Data are
expressed as mean ± SEM from six independent experiments. *,
significant difference (p < 0.001) compared with
eosinophils incubated with serum IgA.
