Effects of anti-lymphocytic globulin in human subjects

Some of the immunological effects of anti-lymphocytic globulin (ALG) were examined in patients taking part in a clinical study of equine ALG in ulcerative colitis. ALG administration led to reduction in the percentage of peripheral blood lymphocytes forming spontaneous rosettes with sheep erythrocytes (E rosettes). Evidence was obtained that this reduction was the result of genuine depletion of circulating T (thymus-dependent) lymphocytes, rather than blockade of E-rosette formation by ALG on lymphocyte surfaces. Using an immunofluorescence technique, horse Ig was demonstrated on lymphocytes from patients receiving ALG. By combining this technique with E-rosette formation, horse Ig was detected on patients' E-rosette-positive and -negative lymphocytes. Horse Ig levels in patients' sera were measured by haemagglutination inhibition, and the sera were also examined for anti-lymphocytic antibodies. Although lymphocyte-binding horse Ig was detectable in teh patients' sera, lymphocytotoxic antibody could not be demonstrated. It can be concluded that lymphocytotoxic antibody was rapidly removed from the serum of patients receiving ALG, by binding to circulating lymphocytes.