Qa gene expression: biosynthesis and secretion of Qa-2 molecules in activated T cells.

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Abstract
The biosynthesis and expresssion of the tissue specific class I molecule Qa-2 have been studied in resting and activated T-cell populations. Polyclonal activtion of T lymphocytes induces a 3-4-fold increase in the biosynthesis of Qa-2 molecules but no increase in cell-surface levels. Analysis of the biosynthetic pathway of the Qa-2 molecule in activated lymphocytes reveals that .apprxeq. 70% of the newly synthesized Qa-2 molecules are secreted as soluble molecules. In resting-cell populations, Qa-2 remains entirely cell-associated. This process is unique to the Qa-2 molecule, since other class I molecules (e.g., H-2Kb and H-2Db) synthesized by activated cells remain cell-associated. The possibility that the secreted Qa-2 molecule is the product of a new Qa gene or an alternatively spliced mRNA is considered. These results indicate that the Qa-2 molecules may not just function as a cell-surface recognition structure but also may serve a role as a soluble factor synthesized by activated lymphoid cell populations.