J. Bruce Smith

Stimulation of autologous and allogeneic human T cells by B cells occurs through separate B-cell antigen systems

Abstract Studies were performed to determine the cell types involved in autologous mixed lymphocyte reactions (AMLR). Separation of peripheral blood leucocytes from normal donors into T-cell and B-cell enriched populations and subsequent co-culture of T cells and mitomycin-C inactivated non-T cells resulted in increased DNA synthesis by the responding T cells. Procedures such as removal of plastic-adherent or phagocytic cells enriched the B-cell content of the stimulator population and also enhanced stimulation of both autologous and allogeneic T cells. Velocity sedimentation separation of peripheral blood leucocytes into large and small lymphocyte fractions showed that cells which stimulate in MLR and AMLR are found in the small cell fraction and that large cells, morphologically monocytes, do not stimulate either reaction. Studies with anti-B-cell antisera obtained from multiparous women showed that the antigens of B cells which stimulate AMLR are distinct from those which stimulate MLR.

Surface phenotype of responder cells in the syngeneic mixed lymphocyte reaction in mice.

Abstract The organ distribution and surface phenotype of SMLR responder cells has been investigated. Nylon-wool-passed spleen cells, which proliferate in response to mitomycin-C-treated syngeneic spleen cells, are Thy 1.2 + Ly 1 + 2 − 3 − . SMLR responder cells are not confined to the spleen since nylon-wool-nonadherent lymph node cells as well as unfractionated thoracic duct lymphocytes show activity. Responder cells have characteristics of mature T cells since cortisone-resistant thymocytes, but not thymocytes from untreated mice, are capable of SMLR response. In addition, naturally occurring thymocytotoxic antibody (NTA), which in our experiments exhibits cytotoxicity only for thymocytes, does not appear to affect the subpopulation of the T cells which respond in the SMLR.

Autologous mixed lymphocyte culture responder T cells are in the concanavalin A reactive subpopulation and separate from alloreactive cells.

Abstract We have characterized the T cells which respond to non-T cells in the autologous mixed lymphocyte culture (AMLC) reaction. Lymphocytes were separated by discontinuous gradient fractionation, and populations were eliminated by treating either concanavalin A (Con-A) or AMLC-responding T cells with Budr and subsequent light exposure. The results show that AMLC-responding T cells occur in gradient fractions showing maximal Con-A responsiveness and that deletion of Con-A responsive cells by Budr followed by light exposure also deletes the AMLC-responding T cells. Con-A and MLC responses of cells remaining after Budr plus light treatment of AMLC were vigorous, although AMLC responses were abrogated. AMLC responses after Budr + light treatment of MLC-activated T cells were comparable to those in control cultures but MLC responses were decreased as expected. Taken together, these results indicate that the T cells which respond in AMLC are a subset of the Con-A responsive T-cell population and that they are separate from MLC-responding T cells.

Primary and secondary autologous mixed-lymphocyte interactions in mice occur via antigens encoded by genes in the I region of the major histocompatibility complex

Abstract The antigens stimulating the autologous mixed-lymphocyte reactions (AMLR) were studied in experiments employing specific blocking antisera and through panels of secondary stimulating cells differing in the MHC. Antisera directed to the entire I region, I-A, I-EC, or AϵEα were all effective in blocking the primary AMLR. A principal role for those determinants encoded in I-A was indicated by secondary stimulation experiments. In secondary cultures, I-EC encoded determinants generated weaker responses in the absence of I-A homology.

Reversible blocking of antibody-dependent cell-mediated cytotoxicity☆

Abstract The ability of human peripheral blood lymphocytes to kill antibody-coated Chang liver cells in antibody-dependent cell-mediated cytotoxicity (ADCC) can be blocked with aggregated IgG (agg-IgG) or by soluble immune complexes. Dissociation of aggregates of IgG or immune complexes from the cell surface, however, resulted in partial recovery of the ability both to bind agg-IgG and to kill in the ADCC assay. Our results indicate that “unblocking” of effector cells could occur in vivo when the concentration of circulating immune complexes is lowered.