Immunological investigations in aplastic anemia patients.

In 53 patients with aplastic anemia (AA) a number of parameters concerning immune responsiveness were analyzed. Severe monocytopenia and B-lymphocytopenia was detected in most patients, especially in those with diffuse lymphocyte infiltration in the bone marrow. T-inducer (OKT4)/T-suppressor (OKT8) ratios were normal. The mean IgG level was significantly decreased. The frequency of specific antibodies to common viruses was comparable to that of healthy donors except for cytomegalovirus to which antibodies were less frequently found. The responding capacity in MLC was normal but patients' lymphocytes were often less stimulating than control lymphocytes. Radioresistant suppressor cells were found in 1 patient. In vitro lymphocyte reactivity to mitogens and antigens was severely impaired, related to the numbers of monocytes present. When allogeneic monocytes were added, mitogen responses could be restored.