Phosphoantigen Presentation by Macrophages to Mycobacterium tuberculosis-Reactive Vγ9Vδ2(+) T Cells: Modulation by Chloroquine

Vγ9Vδ2(+) T cells (γδ T cells) are activated by Mycobacterium tuberculosis and recognize mycobacterial nonpeptide phosphoantigens. The role of antigen-presenting cells in the processing and presentation of phosphoantigens to Vγ9Vδ2(+) T cells is not understood. We analyzed the role of macrophages for activation of γδ T cells by a new synthetic phosphoantigen bromohydrin pyrophosphate (BrHPP) and M. tuberculosis. Macrophages greatly increased γδ T-cell activation by both BrHPP and M. tuberculosis. Fixation of macrophages before infection demonstrated that uptake of M. tuberculosis was required for presentation to γδ T cells. Antigens of M. tuberculosis remained stably associated with macrophage surface and were not removed by paraformaldehyde fixation or washing. Macrophages processed M. tuberculosis for γδ T cells through a brefeldin A-insensitive pathway, suggesting that transport through the endoplasmic reticulum and Golgi complex of a putative presenting molecule is not important in the early processing of M. tuberculosis antigens for γδ T cells. Processing of M. tuberculosis was not eliminated by chloroquine, indicating that processing of γδ antigens is not dependent on acidic pH in the lysosomes. Chloroquine treatment of BrHPP-pulsed macrophages increased activation of γδ T cells. Ammonium chloride treatment of macrophages did not increase reactivity of γδ T cells to BrHPP, indicating that the effect of chloroquine was independent of pH changes in endosomes. Chloroquine, by inhibiting membrane traffic, may increase association and retention of phosphoantigens with cell surface membrane molecules on macrophages.