CD8 T cells are important immunoregulatory cells in animal models of allergic disease, but their role in human allergic immune responses has not been defined. With the development of novel immunotherapeutic reagents, it is clearly important to ascertain whether CD8 T-cell responses are altered following conventional allergen-specific immunotherapy (SIT) and hence targets for future developments/strategies.
To study the allergen-specific cytokine release of freshly isolated CD8 T cells from the blood of separate groups of house dust mite- (HDM) allergic patients, patients post-SIT and control nonatopic donors.
CD8 T cells were isolated by positive selection with immunomagnetic beads and cultured with the affinity purified major mite allergen Der p 1 or with different mitogens, using irradiated autologous peripheral blood mononuclear cells as antigen-presenting cells (APCs). Supernatants were collected at a number of time points and assayed by ELISA for the cytokines interleukin (IL) -4, IL-5 and interferon-gamma (IFNγ).
CD8 T cells stimulated with Der p 1 produced significant quantities of IFNγ with cells from HDM-allergic subjects releasing considerably more IFNγ than cells from nonatopic subjects, an average of 804 ± 283 pg/mL of supernatant compared with 30.2 ± 18.8 pg/mL (P = 0.006). The cytokine was detected in cultures of 16/17 of the allergic subjects and 4/7 of the nonatopic. CD8 T cells from 6/10 patients who had received HDM-SIT released IFNγ at an average of 363 ± 202 pg/mL, which was less than the allergic group but still higher than the nonatopic (P = 0.05). Equivalent levels of IFNγ were detected when the cells were stimulated with the mitogen PHA and this was the same in all groups. Reliable allergen-specific release of significant quantities of IL-4 or IL-5 was not detected from CD8 T cells.
Allergen-specific IFNγ is produced at far greater levels from CD8 T cells of HDM-sensitive allergic patients than from nonatopic control individuals and this level is reduced following SIT.