Survival of memory T cells specific for Japanese cypress pollen allergen is maintained by cross‐stimulation of putative pectate lyases from other plants

In view of recent studies on the mechanisms of the survival of peripheral memory T cells, we tested the biologic role of pectate lyase, a pectin‐degrading enzyme, as the cross‐reactive antigen required for the recurring survival signals for human T cells specific for Cha o 1, a pollen allergen molecule of the Japanese cypress. We determined a 16‐mer epitope peptide for the T‐cell clone, and prepared synthetic oligopeptides of homologous regions in putative pectate lyase of other plants. Of these homologous peptides, ZePel ( Zinnia elegans ), ban 17 (banana), and Amb a 1.1 (short ragweed) induced strong proliferative responses of the Cha o 1‐specific T‐cell clone in vitro . In addition, suboptimal doses of peptide homologs derived from banana and short ragweed enhanced the survival potency of this T‐cell clone without detectable proliferative responses to the peptides. When there was no antigen stimulation, the T‐cell clone decreased in viable cell number and lost antigen‐specific proliferation activity on day 6 during in vitro incubation. On the other hand, T‐cell clones incubated with these survival‐inducing peptides maintained proliferative activity to Cha o 1 even on day 9. Serum derived from the donor patient did not contain detectable levels of IgE specific to banana or short ragweed by CAP‐RAST. These results show that human T cells specific for pollen allergen seem to use cross‐reactive pectate lyase peptides to deliver survival signals even in the absence of pollen allergen, and memory T cells maintained in such a manner might be functioning at the onset of allergic pollinosis, although pollen allergens are seasonal.