The effect of trypsin on CD1a molecule of human thymocytes.

The cortical thymocytes expressed at least three distinct cell-surface differentiation antigens. CD1a (Mr 49,000), CD1b (Mr 45,000) and CD1c (Mr 43,000) which are non-covalently attached to beta 2-microglobulin. In the present study, we confirm the presence of two out of the three CD1 molecules on epidermal Langerhans cells by biochemical analysis. Furthermore some CD1a monoclonal antibodies immunoprecipitated an additional molecule with an apparent relative mass of 27,000 from Langerhans cell-enriched epidermal cell lysates and not from fresh iodinated thymocyte lysates. From trypsin-treated thymocyte lysates, this low molecular weight protein was considered as a cleavage product of Mr 49,000 molecule (CD1a molecule) by this enzyme which is used to obtain epidermal cell suspensions. This Mr 27,000 was found to content one N-linked oligosaccharide residue by endoglycosidase F treatment. On CD1-expressing cells (thymocytes and Langerhans cells) it would be tempting to take advantage of the sensitivity of CD1a molecule to trypsin in order to precise the structure/function relationship of CD1a antigen.