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J. Virol., Nov 1995, 6665-6677, Vol 69, No. 11
LM Mylin, RH Bonneau, JD Lippolis and SS Tevethia
Simian virus 40 large tumor (T) antigen contains three H-2Db-restricted (I,
II/III, and V) and one H-2Kb-restricted (IV) cytotoxic T lymphocyte (CTL)
epitopes. We demonstrate that a hierarchy exists among these CTL epitopes,
since vigorous CTL responses against epitopes I, II/III, and IV are
detected following immunization of H-2b mice with syngeneic, T-
antigen-expressing cells. By contrast, a weak CTL response against the
H-2Db-restricted epitope V was detected only following immunization of H-2b
mice with epitope loss variant B6/K-3,1,4 cells, which have lost expression
of CTL epitopes I, II/III, and IV. Limiting-dilution analysis confirmed
that the lack of epitope V-specific CTL activity in bulk culture
splenocytes correlated with inefficient expansion and priming of epitope
V-specific CTL precursors in vivo. We examined whether defined genetic
alterations of T antigen might improve processing and presentation of
epitope V to the epitope V-specific CTL clone Y-5 in vitro and/or overcome
the recessive nature of epitope V in vivo. Deletion of the H-2Db-restricted
epitopes I and II/III from T antigen did not increase target cell lysis by
epitope V-specific CTL clones in vitro. The amino acid sequence SMIKNLEYM,
which species an optimized H-2Db binding motif and was found to induce CTL
in H-2b mice, did not further reduce epitope V presentation in vitro when
inserted within T antigen. Epitope V-containing T-antigen derivatives which
retained epitopes I and II/III or epitope IV did not induce epitope V-
specific CTL in vivo: T-antigen derivatives in which epitope V replaced
epitope I failed to induce epitope V-specific CTL. Recognition of epitope
V-H-2Db complexes by multiple independently derived epitope V- specific CTL
clones was rapidly and dramatically reduced by incubation of target cells
in the presence of brefeldin A compared with the recognition of the other
T-antigen CTL epitopes by epitope specific CTL, suggesting that the epitope
V-H-2Db complexes either are labile or are present at the cell surface at
reduced levels. Our results suggest that processing and presentation of
epitope V is not dramatically altered (reduced) by the presence of
immunodominant CTL epitopes in T antigen and that the immunorecessive
nature of epitope V is not determined by amino acids which flank its native
location within simian virus 40 T antigen.
Copyright © 1995, American Society for Microbiology
Hierarchy among multiple H-2b-restricted cytotoxic T-lymphocyte epitopes within simian virus 40 T antigen
Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey 17033, USA.
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