Stability of surface H-2Kb, H-2Db, and peptide-receptive H-2Kb on splenocytes

We have used flow cytometry to study the stability and peptide-binding capability of MHC class I (MHC-I) on the surface of normal C57BL/6 mouse T lymphoblasts. The MHC-I molecules on each cell are nearly evenly divided into two populations with mean half-life values of similar to1 and 20 h. Our observations suggest that members of the later contain peptide bound with medium to high affinity. Cell surface MHC-I molecules capable of binding exogenous peptide (thus, peptide-receptive) belong almost entirely to the less stable population. Before erogenous peptide can bind, MHC-I must undergo a change, probably loss of a very low affinity peptide. For MHC-I-K-b, we found that the maximum rate for binding of exogenous peptide corresponds to a t(1/2) value of 12 min. To maintain the 50:50 steady-state distribution of long-vs short-lived MHC-I molecules on the cell surface, similar to 20 short-lived molecules must be exported to the cell surface for each long-lived molecule.