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

Abstract

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 'i5I-labeled Listeria was reduced in a dose-dependent way. The macrophage presentation ofListeria 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 macrophageassociated 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. Macrophages play a central role as antigen-presenting cells in the induction and expression ofimmune responses to most protein antigens (1, 2). It is widely held that an early event in the activation ofT lymphocytes is their recognition ofantigen present on the. macrophage cell surface in association with gene products of the I region of the major histocompatibility locus (3). The precise mechanism, however, by which macrophages handle antigen in an immunologically relevant way remains to be elucidated. By using protein antigens under I-region control, several laboratories have shown that the immunogens appear to be small peptides that the macrophage selects for T cells to recognize (reviewed in ref. 4).To study the mechanism of antigen presentation, we have used a system that involves the quantitation of the antigen-specific, H-21-region-restricted binding of Listeria monocytogenes-immune T cells to macrophage monolayers (5). This system has the advantage that immunogenicity of a macrophagebound antigen can be assessed in a short period oftime, thereby permitting study of antigen-handling events-uptake, ingestion, and catabolism-in their relationship to presentation to immune T cells (6). We have recently shown that recognition of the Listeria immunogen by T cells takes place only after interiorization of the bacteria by the macrophage (6).We now report that the selective inhibition of antigen catabolism by ammonia and chloroquine is associated with a corresponding inhibition of antigen presentation by macrophages. These results supply evidence for an intracellular pathway of antigen handling by macrophages relevant to T-cell recognition of antigen. MATERIALS AND METHODSThe interaction of macrophages with Listeria-immune T cells as well as the handling of heat-killed Listeria by macrophages were studied in culture by methods described in detail in refs. 5 and 6.Macrophages and T cells were isolated fr...

Effect of chloroquine on cellular immune responses of normal and P. knowlesi‐infected rhesus monkeys

“…Rather, a continuous sensitization was noticed. This could be due to the requirement of accessory cells (macrophages) for catabolising the T cell-depending antigen and its presentation to T cells (28). Chloroquine neutralizes the pH of endosomes and prevents the recycling of the surface receptors of macrophages responsible for the presentation of antigen to T cells (29).…”

Diverse regulatory roles for lysosomal proteases in the immune response

“…Lysosomal proteases introduce cleavages in endocytosed antigens, which trigger unfolding and capture of processed antigen by newly synthesised class II MHC molecules [8][9][10]. In addition, removal of the invariant chain (Ii) chaperone requires the action of one or more lysosomal proteases [11,12].…”

Making Antigen Presentable

“…Ag processing required metabolically active macrophages but not protein synthesis. A subsequent study by these same authors reported that Ag processing required acidic intracellular vesicles, thereby establishing that the endosomal/lysosomal pathway was involved (9). Fixation of the macrophages with paraformaldehyde at various points after exposure to Listeria allowed a dramatic demonstration of the kinetics of Ag processing.…”