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Different antibody responses to sheep and chicken red blood cells in mice.

Injections of SRBC in CBA/H mice resulted in more plaque-forming cells in the spleen than did injections of CRBC. Limiting dilution experiments indicated that there were 3.8 times as many precursors of direct anti-CRBC plaques as of direct anti-SRBC plaques and 6.9 times as many precursors of indirect anti-CRBC plaques as of indirect anti-SRBC plaques. 
 
Cell transfer experiments showed that the number of plaques per precursor transferred was smaller for CRBC than for SRBC, indicating poor proliferation of precursors for anti-CRBC plaques. Tissue culture experiments indicated that increasing the number of spleen cells in the culture bottle did not increase the number of anti-CRBC plaques as much as it did the number of anti-SRBC plaques. Further increase in numbers of spleen cells in the presence of CRBC resulted in decline in the numbers of plaques. On the other hand the number of plaques increased in cultures of larger number of spleen cells in the presence of SRBC. The number of anti-CRBC antibody-forming cells derived from a single precursor decreased after day 4, and the number of anti-SRBC antibody-forming cells per precursor exceeded that of anti-CRBC antibody-forming cells per precursor after day 5. Thus it appears that precursors for anti-CRBC plaques did not proliferate as well as those for anti-SRBC plaques in terms of the number of descendants of a single precursor. 
 
These results indicate that proliferation and differentiation of the precursor cells themselves were regulated by the size of the cell population, possibly through the antibody level in their environment.