|
|
||||||||


*
Centenary Institute of Cancer Medicine and Cell Biology, Newtown, Australia; and
Department of Pathology and Immunology, Monash University Medical School, Prahran, Australia
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
| Materials and Methods |
|---|
|
|
|---|
BALB/cCrSlc and C57BL/6 mouse strains and F1 and F2 progeny were bred and maintained at the Monash Medical School Animal Facility under conventional conditions. Mice were housed at 21°C and were fed Barastock mouse chow (Melbourne, Australia) and water ad libitum. Reciprocal outcrosses were performed to produce F1 and F2 progeny. Mice of both sexes were included in all analyses.
Phenotyping
Mice were thymectomized on day 3, killed at 12 wk of age, and assessed for autoimmune gastritis by histological examination of stomachs and by ELISA for H+/K+ ATPase-specific autoantibodies as described previously (9).
Genotyping
DNA of F2 progeny was extracted from kidneys and subjected to an autosomal genome-wide scan at a 15 cM resolution, using 126 microsatellite markers polymorphic between BALB/c and C57BL/6 strains chosen from the Whitehead Institute simple sequence length polymorphism library (12). An analysis of simple sequence repeat polymorphisms was performed as described previously (13).
Linkage analysis
Recombination distances between each marker were determined
using the MAPMAKER/EXP program (14). Lengths of chromosomes and order
of markers were checked against published maps (15). Genotyping errors
were identified manually as double recombinants or by the error
checking function of MAPMAKER/EXP and were reamplified. Two approaches
to linkage analysis were used. To calculate the linkage of individual
markers to autoimmune gastritis, a 3 x 2 contingency table
(
2 test of independence) was applied. The significance
of linkage achieved by this method was tested by creating an
experimentwise threshold using permutation analysis (16). This
threshold is simultaneously valid for all markers of the genome and was
calculated by permuting the phenotype data for every individual 10,000
times. The highest
2 value for each permutation was
collected and subsequently sorted to produce a null distribution of the
test statistic within the whole genome. The distribution allowed the
calculation of an experimentwise 95% critical threshold
(p < 0.05 of type 1 error in entire genome).
Markers with an experimental
2 surpassing the
experimentwise 95% critical threshold were considered significantly
linked to disease.
Interval analysis of linkage to autoimmune gastritis was conducted on two linkage analysis programs. The MapManager/QT program (17) was initially used to perform interval linkage analysis on autoimmune gastritis by entering the trait values as 0 for unaffected mice and 1 for affected mice (Ref. 18; Kenneth Manly, personal communication). The degree of linkage to autoimmune gastritis was reported using a likelihood ratio statistic (LRS) (19). To report the significance of linkage achieved, the program was used to calculate permutation-derived critical threshold values for significant and suggestive linkage, according to Lander and Kruglyaks specifications (20), for the interval analysis using the methods established by Churchill and Doerge (16, 17, 20). A total of 1000 permutations of phenotypes in the dataset were performed. Disease genes were proposed when the significant linkage thresholds set by this program were surpassed. Qualitative trait analysis was also performed on MAPMAKER/QTL 2.0b using the "penetrance scan" function (Ref. 21; new version supplied by Mark Daly of the Whitehead Institute of Biomedical Research), which optimizes a set of penetrances for each genotypic class. Trait values were entered as 0 or 1 for unaffected and affected mice, respectively. Results of the penetrance scan are given as a logarithm of odds (LOD) score, representing the likelihood that data have arisen due to the effect of a quantitative trait locus with optimized sets of penetrances rather than by the effect of chance (under the null hypothesis that the penetrances for all genotypic classes are equal).
MAPMAKER/QTL and MapManager/QT have individual advantages, and the two programs apply slightly different methods to calculate linkage to binary traits. MAPMAKER/QTL is usually regarded as the tool of choice for the analysis of murine datasets, and its penetrance scan function is ideally suited for performing an interval linkage analysis of binary traits. One disadvantage of the program is its tendency to produce artificially elevated LOD scores in large intervals (>15 cM, 21), which greatly limits its utility for calculating significance thresholds by permutation analysis. MapManager/QT has the advantage of being able to accurately calculate the permutation-derived thresholds specific for individual datasets using methods derived from Churchill and Doerge (16).
Both linkage analysis programs were also used to conduct a quantitative trait linkage analysis of the autoantibody titers in gastritic mice to detect possible disease modifier genes. Autoantibody titers of affected mice were log transformed so as to conform to a normally distributed trait, which is assumed by both programs when scanning for quantitative trait loci (QTL). Chromosomewise and experimentwise permutation thresholds (1000 permutations) were derived for the MapManager/QT analysis and were used to report on the significance of linkage. Chromosomewise thresholds were also determined for the MAPMAKERr/QTL analysis by creating 1000 new traits from the permutation of the original log autoantibody titer. Each trait was then used to scan chromosome 4 for linkage. The highest linkage achieved in each scan was sorted to produce significant (95th percentile, p = 0.05) and suggestive (37th percentile, p = 0.63) thresholds.
| Results |
|---|
|
|
|---|
To determine the mode of inheritance and to map the genes causing
susceptibility to autoimmune gastritis in mice, F1 and
F2 populations were produced using the BALB/cCrSlc
(susceptible) and C57BL/6 (resistant) strains. Progeny were
thymectomized on day 3 of life and; at 12 wk, mice were bled for an
assessment of anti-H+/K+ATPase
autoantibodies by ELISA and killed for histological examination of the
stomach. The high incidence of disease, as defined by the coexistence
of infiltrates and autoantibodies, within the F1 progeny
(30/85, 35%; Table I
) demonstrated that
autoimmune gastritis was inherited as a dominant trait. There was a
high concordance in F1 mice between autoantibody production
and mucosal lymphocytic infiltration, with 30 of 39 (77%)
F1 mice with infiltrates also having autoantibodies. All
mice with autoantibodies had infiltrates. The results of the phenotypic
analyses of 165 F2 progeny are illustrated in Fig. 1
, which exhibits the discontinuous
distribution of disease among progeny as the titers of autoantibodies
in the sera formed a bimodal distribution. Titers of >1:50 were
present in 40 of 165 (24%) mice, whereas the remainder had no Ab
detectable at this titration. All of the mice with titers of
autoantibody of >1:50 also had lymphocytic infiltrate of the gastric
submucosa upon histological examination and thus were considered
gastritic (Table I
). Only 9 of 125 (7%) mice with no evidence of
autoantibodies at a dilution of 1:50 had evidence of gastric
infiltration. These mice were initially excluded from the genetic
analysis (Fig. 1
) because the presence of autoimmunity could not be
confirmed. In previous analyses employing in situ DNA nicked-end and
5-bromodeoxyuridine labeling of gastric mucosa in BALB/c strains, there
was no correlation between the titers of autoantibody and the severity
of gastric pathology,4
supporting the evidence presented here that gastritis in this model is
a discontinuous phenotype.
|
|
2 test of independence). This determination allowed us
to eliminate the effects of the sex chromosomes and maternal factors on
EAG. The total disease incidence of 24% in the F2 progeny
was indicative of relatively few disease genes segregating in the cross
(approximately one to two assuming dominant inheritance with no
epistasis). Genetic mapping and marker linkage analysis
An autosomal genome scan of 40 gastritic and 41 nongastritic
F2 progeny was conducted using 126 polymorphic
microsatellite markers with an average marker separation of 15 cM.
Extra unaffected mice (116 in total) and an increased density of
markers were used in areas showing evidence of linkage to disease. When
linkage analysis was performed at each marker using a 3 x 2
contingency table, 11 markers on the distal region of chromosome 4
displayed linkage to EAG that was greater than the 95% experimentwise
threshold derived from the permutation analysis (
2 of
14.84; Table II
). This result provided
strong evidence for the presence of an EAG susceptibility gene in this
region.
|
Interval analysis using MapManager/QT and MAPMAKER/QTL
The permutation thresholds for reporting the significant and
suggestive linkage derived by MapManager/QT in this dataset were
LRS
15.9 and 9.0, respectively. Applying these thresholds, only
two peaks on distal chromosome 4 surpassed the significant linkage
threshold (Fig. 2
). The highest linkage
to disease occurred at D4mit148 (LRS = 18.9). The
second linkage peak occurred further distal on chromosome 4, at
D4mit127 (LRS = 18.8). Suggestive linkage to autoimmune
gastritis was found to occur on chromosomes 6 (D6mit149;
LRS = 14.5), 9 (between D9mit24 and D9mit18;
LRS = 10.6), and 15 (D15mit17; LRS = 9.8) in
decreasing order of linkage (data not shown).
|
4.3) was applied (20). The more proximal linkage
region of the two on chromosome 4 equaled this threshold. In contrast
to the MapManager/QT linkage report, MAPMAKER/QTL linkage values for
the more telomeric peak on chromosome 4 indicated a relatively modest
contribution to autoimmune gastritis (LOD = 3.9).
All three analyses (marker and interval) consistently demonstrated that
the region conferring most susceptibility to autoimmune gastritis lies
on distal chromosome 4, with tightest linkage to D4mit148
(Fig. 2
). Similar results were also obtained when the nine progeny,
which did not have autoantibodies but did have mucosal lymphocytic
infiltration, were included in the group of affected mice and the
analyses were repeated. We have designated this susceptibility gene
Gasa1 (Gastritis Type A susceptibility
locus 1). The mapping data place the disease gene in a 10:1
confidence interval from D4mit308 through to
D4mit343 (
17 cM). Examination of the genotype
frequencies of markers within the Gasa1 interval (Table II
)
indicate that the Gasa1s (c; BALB/cCrSlc) allele
affects the disease in an additive or dominant fashion, with
homozygosity conferring maximum susceptibility to autoimmune gastritis.
The more telomeric linkage region is centered on D4mit127
(Fig. 2
) and may represent the presence of another disease gene. The
BALB/c homozygous genotype at this locus also confers greatest
susceptibility to disease and has a slightly higher penetrance than
Gasa1, although penetrance of the heterozygous genotype at
this locus is considerably reduced. This region has been tentatively
designated Gasa2.
Finally, evidence of suggestive linkage to autoimmune gastritis has
been shown on chromosome 6. According to the genotype ratios at the
marker of highest linkage (Table II
), heterozygosity confers most
susceptibility to disease in F2 progeny. Confirmation of
this gene will require reproduction of linkage at this locus in an
independent mapping study (20).
QTL analysis of autoantibody titers
Autoantibodies to the gastric H+/K+ ATPase pump are not involved in the pathogenesis of autoimmune gastritis (2), and the degree of gastric pathology in neonatally thymectomized BALB/c mice has not been shown to correlate with antiparietal autoantibody titers.4 To determine whether autoantibody titers were affected by distinct modifier genes, a genome scan for QTLs was performed using MAPMAKER/QTL and MapManager/QT analysis of the log autoantibody titers of affected mice (titer of >1:50).
Experimentwise permutation thresholds for significant and suggestive
linkage were determined to be LRS
16.6 and 9.6, respectively.
Using these criteria, only one locus on distal chromosome 4 exhibited
suggestive evidence of linkage (LRS = 10.4). Although the linkage
region mapped to the same chromosomal segment as Gasa2,
inheritance of the C57BL/6 gene predisposed F2 mice to
higher autoantibody titers. Examination of the raw data indicated that
the significance levels were greatly affected by very high titers in
two of only three individual affected mice homozygous for C57BL/6
alleles on distal chromosome 4.
| Discussion |
|---|
|
|
|---|
This study did not find significant or suggestive evidence of linkage to loci on chromosomes 3 and 16, for which linkage to neonatal thymectomy-induced autoimmune oophoritis has been reported previously (24, 25). However, Gasa1 maps within the same chromosomal segment as the susceptibility loci of other murine autoimmune diseases, including Nba1 (systemic lupus erythematosus (SLE)) and Idd11 (type 1 diabetes) (13, 26). In addition, the distal linkage peak on chromosome 4 (Gasa2) also maps within the same chromosomal segment as another type 1 diabetes susceptibility locus, Idd9 (27). These results suggest that these loci may represent common susceptibility genes shared by SLE, type 1 diabetes, and EAG (28, 29).
The Gasa1 genetic interval contains several genes that are
attractive candidates, including the lymphocyte protein tyrosine kinase
(p56lck) Lck (30, 31) and a number of
subcomponents of the complement C1q component (including
C1qa, C1qb, and C1qc) (32). The
p56lck protein is considered a good candidate
for autoimmune disorders because of its role in regulating T cell
activation and thymocyte development through its delivery of
signals via the mature
ßTCR as well as the pre-TCR (33, 34).
Inherited deficiencies in a number of proteins of the classical
complement pathway have been associated with various autoimmune
diseases (35). In particular, C1q deficiencies have been strongly
implicated in both rheumatoid arthritis and SLE (36, 37). It is
hypothesized that C1q plays a role in the clearance of apoptotic cells,
which might otherwise provide a source of previously unencountered self
Ags causing the activation of autoreactive lymphocytes (38). It is
unlikely that any role for C1qa, C1qb, and
C1qc would involve targeting by autoantibodies, because
there is no correlation between the titers of autoantibody and the
severity of gastric pathology in this model.4
The Gasa2 region, which is distal to Gasa1 on chromosome 4, contains a number of promising candidate genes that encode for members of the TNF receptor (TNFR) superfamily, including Tnfr2, Cd30, 4-1BB, and Ox-40 (39, 40, 41, 42). These receptors and their ligands are involved in several aspects of immune regulation, including: enhancement of proliferation, induction of apoptosis, cytokine production, activation, differentiation of T cells, and mediation of T-B cell and T monocyte interactions (43). Of these candidates, Tnfr2 and Cd30 are of particular interest. CD30 appears to play a key role in the negative selection of T cells, as CD30 deficient mice show defects in this process (44). Signaling of cells via the type 2 receptor of TNF promotes the release of proinflammatory cytokines (43), and the dysregulation of TNF and its receptors (TNFR 1 and 2) has been implicated in the pathogenesis of experimental autoimmune encephalomyelitis, type 1 diabetes, and SLE (43, 45).
The genetic and experimental simplicity of the system described here holds great promise in testing these candidates or isolating as yet unidentified genes predisposing to autoimmune gastritis. Unraveling the genetics of this disease will provide us with a greater understanding of the mechanisms responsible for causing autoimmune disorders.
| Acknowledgments |
|---|
| Footnotes |
|---|
2 Address correspondence and reprint requests to Dr. Alan G. Baxter, Centenary Institute of Cancer Medicine and Cell Biology, Locked bag #6, Newtown NSW 2042, Australia. E-mail address: ![]()
3 Abbreviations used in this paper: EAG, experimental autoimmune gastritis; LOD, logarithm of odds; LRS, likelihood ratio statistic; QTL, quantitative trait loci; SLE, systemic lupus erythematosus. ![]()
4 L. M. Judd, P. A. Gleeson, B. H. Toh, and I. R. van Driel. Chronic inflammation in autoimmune gastritis results in disruption of epithelial cell development. Submitted for publication. ![]()
Received for publication December 4, 1998. Accepted for publication February 5, 1999.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
D. K. Y. Ang, T. C. Brodnicki, M. A. Jordan, W. E. Wilson, P. Silveira, B. L. Gliddon, A. G. Baxter, and I. R. van Driel Two genetic loci independently confer susceptibility to autoimmune gastritis Int. Immunol., September 1, 2007; 19(9): 1135 - 1144. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. Lopez-Diaz, K. L. Hinkle, R. N. Jain, Y. Zavros, C. S. Brunkan, T. Keeley, K. A. Eaton, J. L. Merchant, C. S. Chew, and L. C. Samuelson Parietal cell hyperstimulation and autoimmune gastritis in cholera toxin transgenic mice Am J Physiol Gastrointest Liver Physiol, May 1, 2006; 290(5): G970 - G979. [Abstract] [Full Text] [PDF] |
||||
![]() |
W. Jiang, M. S. Anderson, R. Bronson, D. Mathis, and C. Benoist Modifier loci condition autoimmunity provoked by Aire deficiency J. Exp. Med., September 19, 2005; 202(6): 805 - 815. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. V. Franic, L. M. Judd, N. V. Nguyen, L. C. Samuelson, K. L. Loveland, A. S. Giraud, P. A. Gleeson, and I. R. van Driel Growth factors associated with gastric mucosal hypertrophy in autoimmune gastritis Am J Physiol Gastrointest Liver Physiol, October 1, 2004; 287(4): G910 - G918. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. M. Esteban, T. Tsoutsman, M. A. Jordan, D. Roach, L. D. Poulton, A. Brooks, O. V. Naidenko, S. Sidobre, D. I. Godfrey, and A. G. Baxter Genetic Control of NKT Cell Numbers Maps to Major Diabetes and Lupus Loci J. Immunol., September 15, 2003; 171(6): 2873 - 2878. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. J. Roper, R. D. McAllister, J. E. Biggins, S. D. Michael, S. H. Min, K. S. K. Tung, S. B. Call, J. Gao, and C. Teuscher Aod1 Controlling Day 3 Thymectomy-Induced Autoimmune Ovarian Dysgenesis in Mice Encompasses Two Linked Quantitative Trait Loci with Opposing Allelic Effects on Disease Susceptibility J. Immunol., June 15, 2003; 170(12): 5886 - 5891. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. J. Roper, R. Z. Ma, J. E. Biggins, R. J. Butterfield, S. D. Michael, K. S. K. Tung, R. W. Doerge, and C. Teuscher Interacting Quantitative Trait Loci Control Loss of Peripheral Tolerance and Susceptibility to Autoimmune Ovarian Dysgenesis After Day 3 Thymectomy in Mice J. Immunol., August 1, 2002; 169(3): 1640 - 1646. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. Nagayasu, K. Nagakura, M. Akaki, G. Tamiya, S. Makino, Y. Nakano, M. Kimura, and M. Aikawa Association of a Determinant on Mouse Chromosome 18 with Experimental Severe Plasmodium berghei Malaria Infect. Immun., February 1, 2002; 70(2): 512 - 516. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. R. Merriman, H. J. Cordell, I. A. Eaves, P. A. Danoy, F. Coraddu, R. Barber, F. Cucca, S. Broadley, S. Sawcer, A. Compston, et al. Suggestive Evidence for Association of Human Chromosome 18q12-q21 and Its Orthologue on Rat and Mouse Chromosome 18 With Several Autoimmune Diseases Diabetes, January 1, 2001; 50(1): 184 - 194. [Abstract] [Full Text] |
||||
![]() |
L. M. Araujo, A. Puel, C. Gouarin, A. Hameg, J.-C. Mevel, Y. Koezuka, J.-F. Bach, D. Mouton, and A. Herbelin NKT lymphocyte ontogeny and function are impaired in low antibody-producer Biozzi mice: gene mapping in the interval-specific congenic strains raised for immunomodulatory genes Int. Immunol., November 1, 2000; 12(11): 1613 - 1622. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. A. Jordan, P. A. Silveira, D. P. Shepherd, C. Chu, S. J. Kinder, J. Chen, L. J. Palmisano, L. D. Poulton, and A. G. Baxter Linkage Analysis of Systemic Lupus Erythematosus Induced in Diabetes-Prone Nonobese Diabetic Mice by Mycobacterium bovis J. Immunol., August 1, 2000; 165(3): 1673 - 1684. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. Kodaira, T. Mizoroki, H. Shimada, K. Ishii, M. Hosono, and Y. Kumazawa Potential role of bacterial lipopolysaccharides in the development of autoimmune gastritis induced by neonatal thymectomy Innate Immunity, October 1, 1999; 5(5-6): 269 - 278. [Abstract] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |