Studies of virulent, attenuated, and avirulent strains of tubercle bacilli have demonstrated the proficiency of virulent strains to effect degeneration of normal monocytes cultivated in the presence of normal serum. Attenuated strains were less active in this respect, and avirulent bacilli failed to induce monocytic degeneration.

Comparison of the effects of virulent H37Rv with O.T., P.P.D., and a culture filtrate of H37Rv revealed a similarity in action of H37Rv and its filtrate. The action of O.T. and P.P.D. differed from that of H37Rv in that the greatest effect of H37Rv was upon normal cells as opposed to the effect of O.T. and P.P.D. upon immune cells. Additionally, it was demonstrated that immune serum (anti-BCG) protected immune cells against H37Rv but not against O.T. or P.P.D.

The protection of immune cells by heterologous antisera (anti-Salmonella and anti-ovalbumin) as well as by homologous antiserum (anti-BCG) against the degenerative effects of H37Rv indicated a non-specificity in action of serum factors. The ability of the monocytes of animals immunized with BCG and the failure of monocytes of animals immunized with Salmonella rutgers to withstand parasitization with H37Rv, when both types of monocytes were cultivated in immune (anti-BCG) serum, indicated a specificity of cellular resistance.

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