Mapping human T cell epitopes on phospholipase A2: the major bee-venom allergen

Phospholipase A2 (PLA2), the major bee-venom allergen, was purified by gel filtration, inactivated by denaturing, and carboxymethylating its cysteine residues. Peripheral blood mononuclear cells from an individual (HLA-DR2 [15], Dw52, DQ1 and DQ3) allergic to bee stings were used to generate cell lines specific for PLA2 and a control antigen, tetanus toxoid. These lines were 90% CD3+, 64% CD4+ and 20% CD8+ by fluorocytometry analysis. T-lymphocyte epitope mapping done with 12 overlapping synthetic peptides of PLA2 revealed two immunodominant epitopes. These epitopes correspond to amino acid sequences 50 to 69 and 83 to 97 of PLA2. Cytokine interleukin-4 and Interferon-gamma secretion was studied from PLA2- and tetanus toxoid-specific cell lines. Interleukin-4 secretion was common to both cell lines but only tetanus-toxoid cell lines secreted interferon-gamma. No interferon-gamma was found to be secreted by PLA2-specific cell line in response to stimulation by PLA2 or the two immunodominant peptides.