Rosette-forming ability of thymus-derived lymphocytes in humoral and cell-mediated immunity. II. Helper cell activity

Depletion by monolayer binding of specific precursors of antibody-forming cells directed against cellular antigens

Conditions have been established to permit poly-L-lysine (PLL)-attached cell monolayers to adsorb specific antibody-forming cell precursors (AFCP) from immune spleen cell populations as a negative selection technique. In a model system, sheep red blood cell (SRBC) immune spleen cells were adsorbed onto SRBC monolayers and the cells remaining non-adherent transferred to irradiated recipients. Subsequent to SRBC immunization, these recipients showed up to 95% reduction in splenic anti-SRBC plaque-forming cells (PFC) compared with recipients of control cell populations which had not been exposed to a SRBC monolayer. The depletion observed was shown to be antigen-specific and the extent of depletion comparable with that attained by removal of anti-SRBC AFCP as rosettes. The depletion of AFCP directed against mouse (EL4) and human (QIMR-WIL) leucocyte antigens was then examined. Mixtures of spleen cells immune to EL4 and WIL cells were adsorbed onto PLL-attached monolayers of EL4 or WIL cells, and spleen cells remaining non-adherent transferred to irradiated recipients which were then immunized with either of these cell types. Analysis of recipient serum samples by determination of antibody titre and by immunoblotting indicated that the response to the cell type used in the adsorbing monolayer had been specifically depleted while the response to the other cell type remained unchanged or only slightly impaired. The maximum level of depletion occurred on Day 7 after transfer and declined thereafter. The application of this procedure to improve the frequency of production of spleen cell hybridomas directed against leucocyte differentiation antigens is discussed.

The nature of allorosette-forming cells in rats

ARFC appear in the spleen after transplantation of organs or tissues and immunization with nucleated cells between isohistogenic rat strains. The allorosette formation of rat spleen cells and T cells, isolated by an Ig-anti-Ig column, was examined. It has been demonstrated that 90% of ARFC are B cells and 10% are T cells. The allorosette phenomenon can therefore be considered an immune reaction concerning predominantly the B-cell system. Allorosette-forming T cells are discussed to be SD-antigen-recognizing cytotoxic T cells.

Cell-mediated and humoral immune responses in mice. IV. Difference of the functional cell population between helper activity and delayed-type hypersensitivity

Helper activity in the anti-hapten antibody response was studied in mice in reference to the induction of delayed-type hypersensitivity (DTH) to the carrier protein. Mice were immunized either by an i.v. injection of alum-precipitated bovine serum albumin (AP-BSA) plus bacterial endotoxin or by a s.c. injection of BSA in Freund's complete adjuvant, the latter being effective in inducing DTH. The helper activity was estimated by the antibody response to the challenge with dinitrophenylated BSA (DNP-BSA) given at varying intervals after the injection of BSA. The results indicated that the helper activity was independent of DTH to the carrier protein, suggesting that these two activities, are mediated by different populations of functional cells. A low dose of tolerogenic soluble BSA (sBSA) was sufficient to abrogate the helper activity in the response to DNP-BSA. In contrast, DTH to BSA was only partially depressed by the pretreatment with a low dose of sBSA and was completely depressed by a high dose. DTH reactivity in mice pretreated with a low dose of tolerogen and followed by the immunization with BSA in Freund's complete adjuvant was substantiated by the microscopic observation of mononuclear cell infiltration at the site of the test antigen injection. These results suggest that cells involved in the helper function and DTH may be derived from different precursors.

Helper T-cell kinetics and investigation of antigen receptor expression on early and memory T-helper cells

The subcutaneous application of soluble antigen resulted in generation of helper T lymphocytes in the draining lymph nodes, tested 4 days after priming in the adoptive transfer system. Four days later a specific helper T-cell population was detected in the spleen. B-cell activity could be demonstrated 4-5 days after helper T-cell activity in both organs. We investigated the early helper T-cell population and memory T cells with respect to differences in the expression of antigen receptors. No such differences could be detected, either by anti-immunoglobulin-coated Degalan columns or by an antigen-specific rosetting method.

Antigen-binding T cells as helper cells. Separation of helper cells by immune rosette formation

The spleen T cells from mice immunized 6 days earlier with either chicken gamma globulin (CGG) or with donkey erythrocytes (DRC) were rosetted with CGG-coated sheep erythrocytes or with DRC. The immune rosettes (RFC) (antigen-binding cells) were separated from the bulk of nonrosette-forming cells (non-RFC) by 1-g velocity sedimentation and the RFC and non-RFC tested for helper activity in cooperative antihapten responses in vitro. RFC or non-RFC were mixed with normal or hapten-primed spleen cells, challenged with the appropriate hapten-carrier conjugate and cultured for 4 days in Marbrook tissue cultures. The helping activity was quantitated from the numbers of antihapten antibody-producing cells generated per culture. The results show that specific helper cell activity could be selectively recovered in the immune rosette-forming cell population whereas the non-RFC population was depleted of help. These findings indicate that the helper T cells express specific antigen binding receptors.