Antigen‐Ia interaction and the proteolytic processing of antigen: the structure of the antigen determines its restriction to the A or E molecule of the major histocompatibility complex

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Abstract
The effect of a protease inhibitor, leupeptin, on the presentation of hen egg lysozyme (HEL) to cloned T cells was investigated. We found that leupeptin‐sensitive thiol proteases are apparently less involved when HEL is presented by the I‐Ad molecule, than when it is presented by the I‐Ed molecule. This selectivity was more of a function of the antigen than that of the Ia molecule because presentation of denatured or fragmented HEL was not sensitive to leupeptin whereas antigen presentation to a number of I‐A‐restricted T cell clones specific to other antigens was sensitive to leupeptin. These data demonstrate that the particular combination of major histocompatibility complex/nominal antigen recognized by a certain T cell clone may require processing of the antigen molecule through a certain group of proteases and that other combinations are independent of that particular processing pathway. Furthermore, there is a preference for a certain type of processing depending on the Ia molecule involved.