CD8+ T cells implicated in the pathogenesis of allergic fungal rhinosinusitis

Fungi in paranasal sinuses are characteristic and considered a major pathogenic factor in a subset of chronic rhinosinusitis (CRS) patients, known as allergic fungal rhinosinusitis (AFRS). CD8(+) T cells are enriched in AFRS sinuses but their role in fungal-specific responses is unknown. Alternaria alternata- and Aspergillus fumigatus-specific T lymphocyte responses were investigated in 6 AFRS patients, 10 eosinophilic mucus CRS (EMCRS) patients, 10 CRS with nasal polyps (CRSwNPs) patients, 6 allergic rhinitis with fungal allergy (ARFA) patients, and five controls. Fungal-specific proliferation of human peripheral blood mononuclear cells (PBMCs) was studied prospectively. Proliferating cells were examined for CD3, CD4, CD8, and CD25 expression. Relevant clinical characteristics, fungal allergy, detection of fungi in sinuses, and CD4(+) and CD8(+) composition of sinus T cells were also examined. CD4(+) T-cell division to fungi occurred in all samples, regardless of fungal allergy or CRS. Fungal-specific CD8(+) T-cell division occurred in all ARFA and control samples and the majority of CRSwNP patients; however, CD8(+) T cells failed to proliferate in AFRS and EMCRS patients. The CD8(+) T cells from AFRS patients also did not up-regulate the activation marker, CD25, with fungal antigen exposure. Presence of A. alternata- and A. fumigatus-specific CD4(+) and CD8(+) T-cell proliferation in healthy individuals, ARFA, and CRSwNP patients suggests that both T-cell subsets may be important in immune responses to these fungi. In AFRS and EMCRS patients, only fungal-specific CD4(+) T-cell proliferation occurred; hence, a lack of CD8(+) T-cell proliferation and activation in the presence of sinus eosinophilic mucus in these patients, regardless of fungal allergy, is a novel finding. This raises the question whether a dysfunctional CD8(+) T-cell response predisposes to ineffective clearance and accumulation of fungi in the sinuses of susceptible patients.