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-1Ra 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.