Decrease in macrophage antigen catabolism caused by ammonia and chloroquine is associated with inhibition of antigen presentation to T cells

This paper describes the effects of two lysosomotropic compounds, ammonia and chloroquine, on the interaction of mononuclear phagocytes with immune T cells. The uptake and ingestion of Listeria monocytogenes by macrophages were not affected by the drugs; however, the macrophage catabolism of ¹²⁵I-labeled Listeria was reduced in a dose-dependent way. The macrophage presentation of Listeria to T cells, an I-region-dependent phenomenon, was also inhibited. The degree of inhibition of catabolism paralleled that of antigen presentation. The inhibition of antigen presentation took place if the macrophages were treated before and during Listeria uptake; minimal inhibition took place if the macrophages were treated 30 min after Listeria ingestion, at which time a significant amount of bacteria was already catabolized. Our previous studies had shown that the macrophage-associated antigen recognized by T cells became apparent 30-60 min after uptake of Listeria. We conclude that ammonia and chloroquine affected an intracellular handling step required for the expression of the immunogen relevant for T cell recognition.