Skin CD4+ T Cells Produce Interferon-γIn Vitro in Response to Streptococcal Antigens in Chronic Plaque Psoriasis

Recently, we have demonstrated that group A streptococcal antigen reactive T cells are present in the skin lesions of chronic plaque psoriasis. To determine the cytokine profile (interferon-γ, interleukin-4 and interleukin-10) of these T cells in response to streptococcal antigens, T cell lines were cultured from untreated lesional skin of 13 patients with chronic plaque psoriasis and 12 patients with other inflammatory skin diseases. T cell lines were incubated with or without a sonicated heat-killed mixture of group A streptococcal isolates for 18 h in the presence of a transport inhibitor, stained for surface CD4 or CD8 and intracellular cytokine expression, and analyzed by flow cytometry. Psoriatic T cell lines were grown from 10 of 13 patients and were predominately CD4+ (64%-85%) with 10%-32% CD8+ T cells. Variable numbers of CD4+ T cells produced interferon-γ (0.8%-35%, median 13.9) in eight of 10 T cell lines (p <0.02). In contrast, CD4+ T cells in five of 12 T cell lines obtained from disease controls did not produce or produced minimal interferon-γ in response to group A streptococcal isolates; this was significantly different from the psoriatic T cell lines (p <0.05). Small numbers of interleukin-10 positive (0.8%-1.3%) and interleukin-4 positive (2.1%-2.5%) CD4+ T cells induced by group A streptococcal isolates were also present in two out of five and three out of five psoriatic T cell lines, respectively. This was significantly less in each case than the numbers of CD4+/interferon-γ+ T cells (p