Specific depletion of alloreactive cytotoxic lymphocyte precursors

The role of self-Ia antigens in the murine mixed lymphocyte response

Mouse splenic macrophages (M phi) were tested for their ability to potentiate in vitro allogeneic mixed lymphocyte response (MLR) of highly purified syngeneic responder T cells against allogeneic M phi. It was shown that even extremely low numbers of M phi syngeneic to the responder T cells were able to induce significantly stronger MLR. This potentiating effect was demonstrated to be expressed via the self-Ia antigens present on the surface of syngeneic M phi. The functional involvement of self-Ia antigens was substantiated by two approaches: (a) by using monoclonal antibodies specific for I-region determinants of the responder haplotype M phi and (b) by setting up MLR cultures with stimulator M phi of (responder X stimulator) F1 origin which express both self- and allo-Ia antigens. The results obtained in this study demonstrate that the presentation of self-Ia antigens, in conjunction with the recognition of allo-major histocompatibility complex antigens, are required for in vitro primary MLR.

Antibodies against the transferrin receptor block the induction of cytotoxic T lymphocytes. A new method for antigen-specific negative selection in vitro

The induction of cytotoxic T lymphocytes (CTL) specific for alloantigen in a primary mixed lymphocyte culture (MLC) was used as a model system to study the potential usefulness of monoclonal antibodies directed against the murine transferrin receptor in eliminating antigen-activated T cells. Two monoclonal antibodies were used which are able to block the transferrin-mediated uptake of iron by growing cells. One of these antibodies is cytotoxic in the presence of complement (C). Treatment of MLC cells from control, uninhibited cultures with the cytotoxic anti-transferrin receptor antibody plus C completely knocked out all CTL effector activity showing that all of the effector cells expressed the receptor. However, surviving cells from such antibody-plus C-treated populations were not depleted of precursors since they were able to mount a strong CTL response to the original alloantigen upon restimulation. Blocking antibody against the transferrin receptor, in the absence of C, when present during the course of a primary MLC, completely inhibited the generation of effector CTL. Conditions were optimized such that antibody present during the course of the MLC could completely and specifically eliminate all antigen-activated T cells including precursors as assessed by secondary restimulation with the original, plus third-party antigens, in the absence of blocking antibody. This method for producing specifically unreactive T cell populations appears to be superior to previously described techniques.

Cytotoxic T-cell precursors revealed in neonatally tolerant mice

Induction of neonatal tolerance leads to a profound reduction in cytotoxic T-lymphocyte precursor frequencies against the tolerated alloantigen ("tolerogen") as evaluated by limiting-dilution analysis. The curves obtained were linear within the range tested and, thus, did not yield evidence for any dissociation of cytotoxic precursors from regulatory cell populations. However, it could be shown that cytotoxic T-lymphocyte precursor frequencies against the tolerogen increased drastically if the tolerant spleen cells were adsorbed, prior to limiting-dilution culture, on monolayers of syngeneic blasts expressing receptors for the tolerogen but not if they were adsorbed on syngeneic blasts against third-party antigens. This finding implies that cytotoxic precursor cells against the tolerogen are not clonally deleted in tolerant animals but rather are suppressed by a regulatory cell population that is present at high frequency and presumably acts in an anti-idiotypic fashion.