Two human malignant melanoma cell lines, differing in their patterns of HLA-DR antigen expression, were examined for changes in antigen expression following theophylline treatment. In one line, the basal HLA-DR antigen content of which remained constant during culture, theophylline decreased HLA-DR expression, accompanied by morphological changes indicating increased differentiation. In the second line, the surface HLA-DR antigen expression decreased with time during culture and showed no decrease in antigen expression or morphological changes when cultured in the presence of theophylline.

Use of fetal calf serum as a serum supplement in whole blood microcultures of human lymphocytes resulted in a significant suppression of in vitro stimulation with herpes simplex virus (type 1) antigen, purified protein derivative, and phytohemagglutinin. If the response to viral antigen is weak in autologous serum it may be completely missed if cultures are carried out in fetal calf serum.