The genetic control of the antibody response to a synthetic polypeptide antigen designated poly-L(Tyr, Glu)-poly-D,L-Ala--poly-L-Lys [(T, G)-A--L] has been studied in congenic high responder C3H.SW (H-2b) and low responder C3H/HeJ (H-2k) strains of mice. This response is controlled by the Ir-1 gene and is H-2 linked. The method employed was to study the ability of specifically primed or "educated" T cells of each strain to produce cooperative factors for (T, G)-A--L in vitro. Such factors have been shown to be capable of replacing the requirement for T cells in the thymus-dependent antibody response to (T, G)-A--L in vivo. The T-cell factors produced were tested for their ability to cooperate with B cells of either high or low responder origin by transfer together with bone marrow cells and (T, G)-A--L into heavily irradiated, syngeneic (for bone marrow donor) recipients. Direct anti-(T, G)-A--L plaque-forming cells were measured later in the spleens of the recipients. The results showed that (a) educated T cells of both high and low responder origin produced active cooperative factors to (T, G)-A--L, and no differences between the strains in respect to production of T-cell factors could be demonstrated; and (b) such factors, whether of high or low responder origin, cooperated efficiently with B cells of high responder origin only, and hardly at all with B cells of low responder origin. The conclusion was drawn that the cellular difference between the two strains lies in the responsiveness of their B cells to specific signals or stimuli received from T cells. As far as could be discerned by the methods used, no T-cell defect existed in low responder mice and the expression of the controlling Ir-1 gene was solely at the level of the B cells in this case.

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The cellular basis of the genetic control of the immune response to poly(LTyr, LGlu)-polyDLAla--polyLLys [(T,G)-A--L] in SJL (H-2s, low responder) mice has been investigated using T-cell factors. Thymocytes of SJL origin were educated to (T,G)-A--L and tested for their ability to produce an antigen-specific factor capable of cooperating in vivo with bone marrow cells of either SJL or C3H.SW (high responder) origin. SJL T cells were found to be incapable of producing such a cooperative factor, in contrast with results previously obtained with C3H/HeJ (low responders) and C3H.SW strains. Moreover, SJL bone marrow cells did not produce an antibody response to (T,G)-A--L, even when combined with factor produced by high responder (C3H.SW) mice. Thus, both T and B cells appear to be defective in the SJL strain in the response to (T,G)-A--L.

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