Defects of immunoregulation which occur in haemophilia, reflected by numerical changes in T lymphocyte subsets, have been further investigated in functional studies. Polyclonal T-cell activation by the mitogen phytohaemagglutinin (PHA) and specific stimulation by cytomegalovirus (CMV) or herpes simplex type 2 (HSV-2) in previously sensitized subjects were studied in peripheral blood lymphocyte and in T4-cell-enriched cultures. Compared with 12 controls, the responses of 11 patients (nine with haemophilia A and two with von Willebrand's disease) to PHA were significantly reduced both in unfractionated and in T4-cell-enriched peripheral blood lymphocyte cultures. Reduced responses to PHA were found in HIV (HTLV III)-seronegative as well as -seropositive patients. There were no significant differences between the response of patients' unfractionated and T4-enriched peripheral blood lymphocytes to CMV/HSV-2 recall antigen and the control subjects, although there was evident variation in the magnitude of patients' unfractionated and T4-enriched lymphocyte responses.

Serial determinations of the numbers of peripheral blood T-lymphocyte subpopulations (T-helper/inducer and T-suppressor/cytotoxic cells) were made using monoclonal antibodies in 12 patients with haemophilia who were HIV antibody positive. Eleven patients were clinically severe and one clinically moderate. Follow-up studies for 12-42 months in nine patients showed persisting abnormalities in five patients, abnormalities which developed in three patients who were initially normal, and a return to normal findings in one patient who was initially abnormal. The remaining three patients were followed up for 3-4 months; two showed persisting abnormalities and one a return to normal. Persistent generalized lymphadenopathy was found in one patient who showed raised levels of T-suppressor cells initially and low levels of T-helper cells in the follow-up, but low T-helper cells persisting for up to 12 months were not necessarily associated with disease.