Effect of PPD on the Specific Immune Response to Heterologous Red Cells in Vitro

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Abstract
Purified protein derivative of tuberculin (PPD) was found to enhance the primary and secondary immune responses in vitro to heterologous red cells in spleen cells from non-BCG-immunized mice. Even though PPD is a bone marrow-derived (B) cell mitogen the enhanced cellular immune response was specific for the antigen added to the cultures. Secondary IgG responses in vitro to sheep red blood cells required a 100-fold lower concentration of PPD for maximal enhancement as compared to the primary IgM plaque-forming cell response. The presence of adherent cells was required for the synergistic effect between antigen and PPD. The requirement for thymus-derived (T) cells could be partially overcome by PPD, but a full enhancing effect of PPD required the presence of both T cells and macrophages. It is likely that the antigen, but not the PPD, effect requires the presence of the helper cells. PPD and red cell antigens cooperated in a synergistic rather than an additive fashion when enhancing the specific immune response. In comparison with other B cell mitogens, such as LPS and pneumococcal polysaccharide SIII, PPD was found to be the most effective agent in increasing the primary immune response in vitro. The findings suggest that a nonspecific B cell mitogen and specific antigen can cooperate in increasing the magnitude of a specific immune response.

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