Two distinct azobenzenearsonate-specific helper T-cell subpopulations mediate different forms of T-B cooperation.

Popliteal lymph node T cells from mice footpad-primed with azobenzenearsonate (ABA)-protein conjugates were able to help the anti-trinitrophenyl (TNP) and anti-ABA plaque-forming cell (PFC) responses of normal syngeneic spleen cells cultured in vitro with TNP-ABA-keyhole limpet haemocyanin. Enrichment in ABA-specific helper cells was obtained by positive selection of ABA-primed T cells on ABA-pulsed syngeneic macrophages. The ABA-specific T cells induced by ABA-protein priming are able to help the anti-TNP PFC response of normal B cells through recognition of the ABA determinant either unlinked to TNP (ABA and TNP separately presented to T and B cells) or linked to TNP (ABA and TNP presented as moieties of the same molecule). These two mechanisms of T-B cooperation are mediated by two different ABA-specific helper T-cell subpopulations, which can be distinguished by their different radiosensitivities: the former mechanism is mediated by radioresistant T cells, whereas the latter is mediated by radiosensitive T cells. Both helper T-cell subpopulations bind the ABA-pulsed syngeneic macrophages, demonstrating the presence of ABA-specific receptors on both cell types.

Synergism between two helper cell subpopulations characterized by different radiosensitivity and nylon adherence.

The present work extends our previous results on the radiosensitivity of the helper cell function. Two helper cell subpopulations, 1 radiosensitive and the other radioresistant, have been demonstrated in the spleen of mice at different times after priming with HRBC. The radiosensitive subpopulation increases with the increasing time interval between carrier-priming and irradiation. The 2 cell subpopulations have been further characterized by different nylon adherence properties: radioresistant helper cells adhere to nylon wool, whereas radiosensitive cells pass through. The 2 cell subpopulations were separated by x-irradiation and nylon wool filtration, and their helper activity was assessed separately or after recombination. The results favor the notion that 2 functionally independent helper T cells, as characterized by different radiosensitivity and nylon adherence, participate synergistically in the helper activity of primed spleen cells.

Radiosensitivity of the helper cell function.

The helper function of T cells primed and irradiated in vivo was tested in vitro by the Mishell-Dutton technique. Spleen cells from mice carrier-primed with HRBC and exposed to 50 to 2000 rads of x-radiation were assayed for their ability to help syngeneic normal spleen cells to mount an in vitro anti-hapten antibody response after stimulation with the conjugate TNP-HRBC. The anti-TNP response was evaluated by the Jerne technique. The helper activity was titrated by adding graded numbers of carrier-primed spleen cells to a constant number of normal spleen cells. The slope of the initial linear portion of the response-cell dose titration curve was taken as an estimated of the helper activity and found to decrease with increasing the x-ray dose. The curve describing the remaining helper activity as a function of the radiation dose shows the presence of two components, one radiosensitive, the other, radioresistant. This suggests the existence either of helper cells at different stages of activation or of two cell subpopulations participating in the helper function.

In vitro immune response of spleen cells from mice genetically selected for high or low antibody production.

The aim of this study was the identification of the cell type in which genes selected for high or low response to SRBC express their functions. Spleen cells from high (H) and low (L) responder mice were immunized with SRBC in the Mishell and Dutton system. An antibody response of different magnitude was found in cultures of H and L spleen cells, the difference being at least as great as that observed in vivo. This finding under experimental conditions allowing the exclusion of any influence of the animal milieu during the immune response, suggest macrophages, B, and T lymphocytes as possible target cells of gene action. In vitro cell separation and recombination experiments in which spleen cells were immunized with SRBC, TNP-LPS, or TNP-HRBC indicate that the genetic differences between H and L responders brought about by selective breeding are expressed in lymphocytes to greater extent than in macrophages. The role of histoincompatibility in the recombination experiments in unlikely but cannot be excluded. Among lymphocytes, B cells but not helper T cells were found more responsive in cultures of spleen cells from H than from L mice.