Two different mechanisms for the inhibition of rosette formation in mice.

The vast majority of spleen T cells (T.sRFC) which spontaneously bind to sheep red blood cells (SRBC) in an antigen-specific fashion express the Thy-1+, CD3+, CD8+ phenotype. Inhibition of rosetting by antibodies to surface molecules occurs via distinct mechanisms according to the antibody. CD8 and CD3 molecules are located in proximity to SRBC receptors and steric hindrance is the most likely explanation for the inhibition of rosetting by antibodies to these molecules. On the other hand, anti-Thy-1 antibody bound to T.sRFC induces a dynamic process involving intracellular cAMP, and which results in the inaccessibility of SRBC receptors. Thymulin could restore normal sensitivity of T.sRFC from adult thymectomized (A.Tx) mice to all inhibitory antibodies whatever the mechanism by which they hinder rosette formation. These results reinforce the idea that thymulin may act on membrane characteristics.