Immunological Identity of the Small Subunit of HL-A Antigens and β 2 -Microglobulin and Its Turnover on the Cell Membrane

A number of immunological methods have been employed to show that the small subunit of HL-A antigens, isolated either after papain treatment or after solubilization with detergent, is identical to β2 -microglobulin, a protein previously isolated from human urine and shown to be homologous in structure to constant region domains of immunoglobulins. Moreover, quantitative data indicate virtually total identity between the small subunit of HL-A antigens and β2 -microglobulin. Studies of the turnover of labeled HL-A antigens from the lymphocyte surface indicate that the two subunits turn over at similar rates, although only the small subunit could be detected in the culture medium. The significance of these observations is discussed.