CD26 expression in leprosy and other granulomatous diseases correlates with the production of interferon-gamma.

Background: Leprosy represents a spectrum of clinical manifestations that reflect the immune response to antigens of Mycobacterium leprae. The tuberculoid form of leprosy, which is characterized by an organized development of granulomas, has recently been correlated with a Th1-like immune response. The lepromatous form of leprosy, with a characteristic lack of cellular immunity, has been correlated with a Th2-like immune response to mycobacterial antigens. Dipeptidylpeptidase IV (CD26) is an ectopeptidase that is expressed in various tissues; in the hemopoietic system, it is predominantly expressed by T cells.
Experimental Design: We stained frozen sections of skin biopsies obtained from patients with different forms of leprosy, sarcoidosis, and Piringer's lymphadenitis. Sections were stained for interferon-gamma (IFN-gamma) and CD26 with the alkaline phosphatase anti-alkaline phosphatase technique and in two-color stainings by immunofluorescence.
Results: We found strong signals for IFN-gamma and for CD26 in all investigated cases of tuberculoid leprosy. In contrast, in all biopsies taken from patients with lepromatous leprosy, we found no or very weak signals for these antigens. By immunofluorescence double-labeling, we could show that IFN-gamma and CD26 were expressed by the identical cell population. We confirmed this correlation of CD26 expression and IFN-gamma production in other granulomatous inflammatory reactions such as sarcoidosis and Piringer's lymphadenitis.
Conclusions: From our results, we conclude that a high expression of CD26 may be suggestive of Th1-like immune reactions.