Allogeneic transplant recipients with GVHD showed reduced HSV-1–specific antibody production. HSV-1–specific IgG1 (A) and IgG2a (B) antibodies in the BAL fluid were determined by ELISA 14 days after intranasal HSV-1 infection. Data represent means ± SE of individual or pooled BAL samples, derived from at least two separate experiments. Numbers of mice were: 5 (normal CBA), 4 (allogeneic GVHD), and 10 (allogeneic no GVHD). The asterisks indicate a significant difference from both normal CBA and allogeneic no GVHD (P < .04; Student's t-test) for IgG2a, and a significant difference from normal CBA (P < .02; Student's t-test) for IgG1.