DECREASED NUMBER OF CD73 (ECTO-5'-NUCLEOTIDASE) MOLECULES ON LYMPHOCYTES FROM PATIENTS WITH PRIMARY IMMUNOGLOBULIN DEFICIENCIES - CORRELATION BETWEEN NUMBER OF CD73 MOLECULES AND T-LYMPHOCYTE FUNCTION IN-VITRO

CD73 is a bifunctional glycosyl phosphatidylinositol anchored leucocyt e differentiation antigen which has specific ecto-5'-nucleotidase (ect o-5'-NT) activity and is an accessory T-lymphocyte activation molecule . The aim of the present study was to investigate the CD73 expression on blood mononuclear cells (BMC) from a group of patients with primary immunoglobulin deficiency (IGD). This group of patients had both sign ificantly decreased levels of ecto-5'-NT on BMC (P = 0.002) and decrea sed numbers of CD73 molecules per CD73(+) lymphocyte (P = 0.01). Five of the 10 patients had a decreased percentage of CD73(+) lymphocytes. Among B-lymphocytes the patients had normal percentages of CD73(+) cel ls but four of the 10 patients had numbers of CD73 molecules per CD73( +) B-lymphocyte below the normal range. Among CD4-lymphocytes three ou t of 10 patients had percentages of CD73(+) below the normal range and four out of 10 patients had decreased percentages of CD73(+) CD8-lymp hocytes. Significant correlations were found between in vitro prolifer ative responses to mitogens and the number of CD73 molecules per CD73( +) lymphocyte (r(s) = 0.60, P < 0.01) and per CD73(+) CD8-lymphocyte ( r(s) = 0.64, P < 0.02). In addition, a positive correlation was found between ability to proliferate and level of ecto-5'-NT on BMC (r(s) = 0.53, P < 0.05). Furthermore the ability of BMC to synthesize ecto-5'- NT was studied. During: 2 days' culture ecto-5'-NT activity increased markedly on BMC from both patients and healthy donors. The level of ac tivity on BMC from all patients attained levels higher than on freshly isolated BMC from healthy donors. This shows that the decreased level s of ecto-5'-NT found on freshly isolated BMC from patients with IGD i s due to defective regulation of the enzyme activity in vivo.