Immune response to atypical mycobacteria: immunocompetence of heavily infected mice measured in vivo fails to substantiate immunosuppression data obtained in vitro.

The results of in vitro experiments designed to measure the immunocompetence of mice heavily infected with the atypical mycobacterial pathogens Mycobacterium avium and Mycobacterium simiae were compared with the results of experiments which used in vivo approaches. Blastogenic responsiveness in vitro both to mitogen and to alloantigen was severely depressed in the heavily infected mice; this responsiveness could be restored by removal of an inhibitory Thy-1.2-, nylon wool-adherent cell population. No evidence was found to support the previous contention that suppressor T cells may play a role in the inhibition of this responsiveness. These results were then compared with experiments which measured the ability of the infected animal to elicit a delayed-type hypersensitivity response to sheep erythrocytes in vivo. However, although delayed-type hypersensitivity responses in vivo were also depressed, evidence was obtained which suggested that this unresponsiveness was due to inadequate sensitization of T cells, possibly due to catabolism of antigen, rather than due to the influence of an active, immunosuppressive mechanism. Finally, despite the severely depressed ability of cells from infected mice to respond to alloantigenic stimulation in vitro, infected animals were fully able to cause the regression of a tumor implant in vivo.