Detection of soluble class i molecules (non hla‐a or hla‐b) in serum, spleen membranes and lymphocytes in culture

Abstract

Soluble major histocompatibility complex class I molecules (sHLA) present in human serum can be resolved by gel filtration into two different peaks with an apparent molecular mass of about 200 kDa (30% of the total) and 50–60 kDa (60%–70%). The serological analysis of the peaks shows that A or B specificities can only be detected in the 200 kDa peak while both are recognized by the monomorphic W6/32 monoclonal antibody (mAb) and anti‐β₂‐microglobulin mAb. Such sHLA (non HLA‐A or ‐B) molecules are released from human spleen membranes upon incubation at 37 °C and have been purified by affinity chromatography with mAb W6/32 bound to Sepharose. The molecular mass analysis by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis of the sHLA (non HLA‐A or ‐B) and of the classical HLA‐A or ‐B antigens still bound to the membranes and purified from the same membranes after detergent solubilization does not show a significant difference, indicating that sHLA do not represent proteolytic fragments of the classical HLA‐A or ‐B antigens. The presence of sHLA (non HLA‐A or ‐B) has also been detected in the supernatants of lymphocyte cultures and increases dramatically upon stimulation by mitogens. The effect of pokeweed mitogen, phytohemagglutinin, Staphylococcus aureus Cowan strain and phorbol 12‐myristate 13‐acetate on the secretion of sHLA has been studied. The molecular mass of the secreted sHLA (detected using [¹⁴C]leucine) is compared with the classical transmembrane proteins.