AbstractThe distribution has been studied of the foci of antibody‐secreting cells in the spleens of mice responding to two different haptens, 4‐hydroxy‐5‐iodo‐3‐nitro‐phenacetyl (NIP) and 2,4‐dinitrophenyl (DNP) on identical or different carriers, using a sensitive focus assay technique.Mice were irradiated and repopulated with an excess of spleen cells from donor mice primed with the two haptens and a limiting number of cells primed to one carrier. The recipient mice were then challenged with both haptens, each conjugated to a different sample of the identical carrier. The incidence of monospecific foci occurring in different areas of the spleen was 21 % for each hapten, and the coincidence of foci directed to the different haptens occurring in the same area of the spleen was about 31%. This distribution was not significantly different from that seen in experiments when a further population of cells primed to a second carrier was also injected, followed by challenge with the two haptens conjugated to the different carriers. Experiments in which small fragments of the spleens were cultured confirmed, in the single carrier system, the presence of regions in which antibody to one hapten only was secreted, and of other regions in which antibodies to both NIP and DNP were secreted.These results support the hypothesis that cooperation is an extremely local and selective phenomenon, such that in our system one effective T cell is able to help only one B cell precursor to develop into a clone of antibody
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