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Correspondence to: Howard M. Grey, Division of Immunochemistry, La Jolla Institute for Allergy and Immunology, 10355 Science Center Dr., San Diego, CA 92121. Tel:619-558-3561 Fax:619-558-3525
H-2K mice injected, intravenously in saline or intraperitoneally in incomplete Freund's adjuvant, with large quantities of the immunodominant I-Ekrestricted epitope from moth cytochrome c (MCC) 88103 fail to respond to subsequent immunization with this epitope when administered in complete Freund's adjuvant. This state of tolerance can be broken by immunization with certain MCC 88103 analogues that are heteroclitic antigens as assessed on representative MCC 88103 specific T cell clones. In this paper, the mechanism of breaking tolerance by heteroclitic antigens was investigated. The following observations were made: (a) T cell hybridomas derived from tolerance-broken animals required higher concentrations of MCC 88103 to be stimulated than hybridomas derived from normal immune animals, suggesting that they have T cell receptors (TCRs) of lower affinity; (b) in contrast to normal immune animals whose MCC-specific TCRs are typically Vß3+/V
11+, none of the hybridomas derived from tolerance-broken animals expressed Vß3, although they were all V
11+. Also, the Vß complementarity determining region 3 (CDR3) regions from the tolerance-broken animals did not contain the canonical structure and length characteristics of the normal MCC 88103 immune repertoire; and (c) adoptive transfer and tolerization of MCC-specific Vß3+/V
11+ transgenic T cells followed by immunization with heteroclitic antigen failed to terminate the state of tolerance. Collectively, these data strongly suggest that the mechanism involved in breaking tolerance in this system is the stimulation of nontolerized, low-affinity clones, rather than reversal of anergy. Further support for this mechanism was the finding that after activation, T cells apparently have a lowered threshold with respect to the affinity of interaction with antigen required for stimulation.
Key Words: molecular mimicry, cytochrome c, T cell repertoire, tolerance
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