B Cell Function in Human Marrow Transplant Recipients Assessed by Direct and Indirect Hemolysis-in-Gel Assays

Abstract

B cell function was studied in 35 healthy controls and 42 individuals who were recipients of bone marrow transplants for aplastic anemia or hematologic malignancy. Lymphocytes were stimulated in vitro by killed Staphylococcus aureus bacteria (Staph. aureus). Antibody secretion was measured as plaque forming cells (PFC) in a direct hemolysis-in-gel assay by using fluorescein isothiocyanate (FITC)-coupled sheep red blood cells (SRBC) and in an indirect assay with protein A coupled SRBC and antisera against human IgG, IgA, and IgM. A pH of 7.5 in culture was crucial for optimal antibody secretion to occur. Lymphocytes from patients studied during the first 3 months after transplantation (short-term patients) had lower cell survival after 6 days in culture than that of lymphocytes from healthy controls, whereas cell survival of lymphocytes from patients studied more than 1 year after transplantation (long-term patients) was equal to that of controls. Short-term patients tested in the direct assay showed a mean of 12 ± 4 [S.E.] PFC/10⁶ cells compared to a mean of 300 ± 91 PFC/10⁶ in the controls (p < 0.01). The mean number of PFC/10⁶ in long-term patients was 310 ± 222. In healthy controls, the direct assay detected about 4% of the IgM-producing B cells found in the indirect assay. Twelve short-term patients were studied with both assays. None of the patients had PFC with the direct assay, but 11 showed some PFC in the indirect assay. The indirect PFC responses after stimulation by Staph. aureus were significantly lower for patients than for controls (IgG p < 0.05, IgA p < 0.01, IgM p < 0.01). In summary, short-term marrow graft recipients had deficient B cell responses in vitro, but in long-term patients this function was normal.