Activation-Related Differences in HLA Class I-Bound Peptides: Presentation of an IL-1 Receptor Antagonist-Derived Peptide by Activated, but Not Resting, CD4+ T Lymphocytes

We have compared by reverse phase HPLC the set of peptides eluted from HLA class I molecules in resting and activated CD4⁺ Jurkat cells. Two peptides were identified that are presented de novo upon activation. After sequencing, one of these peptides turned out to derive from IL-1R antagonist (IL-1Ra). In keeping with this observation, we found that activated, but not resting, Jurkat cells express IL-1Ra. These data indicate that activation of a CD4⁺ T cell line may result in presentation of peptides derived from proteins expressed de novo after activation. Since IL-1 Ra was not known to be expressed by cells of the T lineage, we also investigated its pattern of expression in normal T lymphocytes. Reverse transcriptase-PCR analyses allowed us to demonstrate that IL-1Ra is expressed upon activation by normal CD4⁺ lymphocytes from peripheral blood and by thymocytes, but not by CD8⁺ T cells. Interestingly, of the two forms of IL-1Ra that have been detected in different cell lineages, the intracellular one and the secreted one, only the former is expressed by activated CD4⁺ T cells.