Effects of T mitogens on in vivo antibody production to a T-dependent antigen in lines of mice genetically selected for high or low in vitro responsiveness to PHA

Genetic regulation of the specific and non-specific component of immunity

Bi-directional selective breeding for antibody (Ab) responsiveness to heterologous erythrocytes (Selection I) produced a high (H) and a low (L) responder line of mice which were also remarkably separated for Ab responses to many unrelated natural antigens (Ags) such as heterologous proteins, viruses, bacteria, parasites and haptens carried by these immunogens. The character "quantitative Ab responsiveness" is controlled by several independently segregating loci (polygenic regulation). The major genetic modification is produced at the level of macrophage activities. The Ag is slowly catabolized and persists for a long time on the macrophage membrane of the H line, whereas it is rapidly destroyed in L line macrophages. The bactericidal and bacteriostatic activity of the macrophage is also strong in the L line and weak in the H line. The opposite genetic regulation of Ab responsiveness and macrophage activity is a fundamental phenomenon for understanding natural and vaccination-induced anti-infectious immunity. The L line is more resistant than the H line against the infections due to intracellular microorganisms (Salmonellae, Yersinia, Mycobacteria, Brucellae, Leishmania) where the macrophage plays the dominant defensive barrier. The H line is more resistant than the L line to the extracellular microorganisms which are efficiently counteracted by a strong antibody response (Pneumococcus, Klebsiella, Plasmodia, Trypanosoma). The intensity of T cell-mediated immunity as measured by delayed type hypersensitivity, which is independent of the genetic regulation of antibody responsiveness, is correlated with the degree of nonspecific inflammation produced at the site of the reaction by the Ag injection in non-sensitized mice.(ABSTRACT TRUNCATED AT 250 WORDS)