Studies on brain-thymus cross-reactive antigens.

An antigen(s) shared by mouse brain and thymocytes was studied with the use of a rabbit anti-mouse brain antiserum (RAMB). Full complements of brain-thymus antigen were found on the brains of several mouse strains, including athymic mice, regardless of their theta antigen genotype. Brain-thymus antigen(s) was absent in newborn mouse brains and gradually reached adult levels two weeks after birth. Treatment of mouse brain with trypsin neither decreased nor increased the amount of the brain-thymus antigen available for absorption of RAMB. Mouse brain-thymus antigens were present on rat thymocytes, but not rat brain. The concentrations of brain-thymus antigens were 3- to 4-fold higher in gray matter than white matter. Cross-absorption studies with RAMB and anti-theta antiserum suggest that theta antigen and brain-thymus antigen are two distinct substances, both antigenically and in their anatomical localization on brain cells.