Nonadherent mouse spleen cells exhibited poor viability and little or no capacity to form antibodies to sheep red cells in the Mishell-Dutton culture system. Viability and antibody-forming capacity could be restored by addition to these cultures of low concentrations of mercaptoethanol (10–4–10–5 M), or by addition of appropriate numbers of mouse peritoneal macrophages. Macrophage concentrations lower than optimal resulted in lower lymphoid cell viability and correspondingly fewer plaque-forming cells, whereas excess macrophages resulted in marked inhibition of antibody formation despite good viability of the lymphocytes. Restoration of the nonadherent cells with mercaptoethanol was thus much simpler and more reproducible than it was with macrophages; furthermore, the number of plaque-forming cells developed in cultures restored with mercaptoethanol was approximately fourfold higher than it was in cultures restored with optimal numbers of macrophages.

In the presence of mercaptoethanol, the plaque-forming capacity of the nonadherent spleen cells was not increased when small numbers of macrophages were added to the system, nor was it decreased when the few macrophages present in the nonadherent cells were further reduced or eliminated. Excess macrophages inhibited antibody formation in the cultures containing mercaptoethanol as they did in control cultures.

Optimal restoration of plaque-forming capacity to the nonadherent spleen cells with mercaptoethanol required the reducing agent to be present throughout the 4 or 5 day culture period. Addition of mercaptoethanol 1 or more days after initiation of culture, or transfer of the cells to a medium free of mercaptoethanol before completion of the culture resulted in a reduction in the numbers of plaque-forming cells.

The results suggest that mouse lymphoid cells do not require macrophages in order to form antibodies to sheep red cells in vitro, provided mercaptoethanol is present in the culture medium. The mechanism of action of mercaptoethanol under these conditions is not completely clear, but one of its effects is to promote the viability of lymphoid cells in the cultures.

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