Identification and quantitation of interferon-γ producing T cells in psoriatic lesions:: Localization to both CD4+ and CD8+ subsets

Interferon-gamma (IFN-gamma) produced by lesional T cell clones is critical for the induction into G1 of the cell cycle by psoriatic keratinocyte stem cells; however, direct data demonstrating psoriatic lesional T cell subset IFN-gamma expression, and quantitation at a single cell level to calculate in vivo proportions, are lacking. In this study, using flow cytometry of freshly isolated normal and psoriatic lesional T cells from keratome biopsies, we found elevated CD3(+), CD4(+), and CD8(+) T cells in all compartments of psoriatic skin, compared with normals. Using Brefeldin A to induce short-term intracellular accumulation of IFN-gamma in T cells capable of IFN-gamma production, we found that 90% of psoriatic patients have IFN-gamma-producing T cells at a greater proportion of their CD3(+) cells than normals, with a mean of 16% +/- 3%, as compared with 4% +/- 2% in normal epidermis (p = 0.01), Expressed as density in the tissue, the IFN-gamma(+) CD3(+) cell number in psoriatic epidermis was 97 +/- 22 per mm(2) surface area, as compared with 4.4 +/- 1.8 per mm(2) of normal epidermis (p = 0.002). Thus, the total number of IFN-gamma(+) CD3(+) T cells in the skin of a patient with 20% involvement is estimated to be 3.9 X 10(8). CD4(+) and CD8(+) IFN-gamma(+) T cells were both elevated in psoriatic kepidermis (p = 0.04 and p = 0.008, respectively) relative to normal skin. In the dermis, only 44% of patients demonstrated a higher percentage of IFN-gamma-producing T cells than did normals (p = 0.1), possibly indicating dilution, in some patients, by fresh infiltrating T cells. Interleukin-4 was not found by a combination of flow cytometry, reverse transcriptase-polymerase chain reaction, western blot, and immunoprecipitation. In conclusion, a significant portion of lesional T cells in psoriasis are IFN-gamma producing, without interleukin-4. The increased numbers of both IFN-gamma(+) CD4(+) and IFN-gamma(+) CD8(+) T cells indicate that both CD4(+) and CD8(+) IFN-gamma(+) T cells are present in appropriate anatomic locations to sustain the lesional pathology.