Uptake and processing of glycosylated mycolates for presentation to CD1b-restricted T cells

Antigen presenting cells (APCs) expressing CD1b mediate the specific T cell recognition of mycobacterial lipid antigens. These lipid antigens require internalization by APCs prior to presentation, but the detailed mechanisms of uptake and intracellular processing are not known. Here we have examined several steps in the presentation of two related classes of CD1b-presented antigens, free and glycosylated mycolates. T cell recognition of glucose m onomycolate (GMM) was blocked by agents that fix APC membranes or neutraliz e the pH of endosomes, indicating a requirement for GMM uptake into an acid ic compartment prior to recognition. Different T cell lines responded to fr ee mycolate or GMM without crossreactivity, yet both antigens were taken up by APCs at the same rate. This demonstrated that differential recognition of these antigens resulted from T cell specificity for their hydrophilic ca ps and that APCs were unable to interconvert these antigens by enzymatic or chemical deglycosylation or glycosylation. APCs were also unable to cleave mycobacterial trehalose dimycolate (TDM) at its most chemically labile lin kages to yield antigenic free mycolates or GMM. Our results indicate that t hese mycolate-containing antigens are resistant to chemical or enzymatic cl eavage by APCs, suggesting that molecular trimming is not a universal featu re of lipid antigen processing. (C) 1999 Elsevier Science B.V. All rights r eserved.