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1 and V
2 Cells in Human Peripheral Blood Mononuclear Cells: TCR Selection Is Not Altered by Stimulation with Gram-Negative Bacteria


*
Pathology Research Laboratory, Massachusetts General Hospital, Charlestown, MA 02129;
Chair of Semeiotica Medica, Catholic University, Rome, Italy;
Vincent Memorial Obstetrical Service, Massachusetts General Hospital, Boston, MA 02114
Despite the enormous potential repertoire of 
T cells, there
are several observations which suggest that the expressed 
repertoire in the periphery of normal individuals is often quite
restricted. To assess selective expansions among 
T cells from
both adult and newborn blood samples, PBMC from 12 normal adults and
cord blood from 15 normal newborns were analyzed for TCRDV1 and TCRDV2
junctional diversity by CDR3 size spectratyping and single-strand
conformational polymorphism. Although TCRBV usage showed extensive
heterogeneity in adults and newborns, both populations often showed
CDR3 region restriction for TCRDV1 and TCRDV2. Analysis of the CDR3
spectratype patterns of newborn twins suggested that clonal selection
for TCRDV is independent of genetic background. The possible role of
Gram-negative bacteria in driving selective responsiveness of 
T
cells in PBMCs from adults was examined by in vitro stimulation with
Escherichia coli and Pseudomonas aeruginosa.
Donors whose TCRDV repertoire was highly clonal in the unstimulated
blood cells showed the same predominant clones among the
bacteria-stimulated cultures. In individuals whose 
T cells were
less restricted, in vitro stimulation did not select for clonality;
rather, the TCRDV repertoires were similar before and after bacterial
stimulation. Together, these data indicate that 
T cells are
often clonally restricted in adults as well as in newborns and suggest
that the prominent stimulatory activity of Gram-negative bacteria does
not by itself account for the restriction or diversity of the 
T
cell repertoire.
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