Changes in airway inflammatory cell populations in Standardbred racehorses after interferon-alpha administration

Natural human interferon-alpha (nHuIFNα) was administered to actively training Standardbred racehorses with inflammatory airway disease (IAD). Inflammatory airway disease was characterized by poor exercise performance and inflammation and exudate in the upper and lower airway. Placebo, 50, 150, or 450 units (U) of nHuIFNα was administered orally for 5 consecutive days to eight horses per treatment group in a double-blind, randomized block design. Response to nHuIFNα was monitored by semiquantitative endoscopic examination score and cytologic examination of bronchoalveolar lavage fluid (BALF) performed at baseline (Day 1), Day 8 and Day 15 after initiation of nHuIFNα administration. Neutrophil, macrophage, lymphocyte, and nucleated cell counts in BALF were lower (P < 0.05), compared with BALF cell counts in placebo-treated horses, 8 days after administration of 50 U and 150 U nHuIFNα, and 15 days after administration of 50 U nHuIFNα. Neutrophil, lymphocyte and nucleated cell counts were lower than cell counts from placebo-treated horses, 8 days following administration of 450 U nHuIFNα. The proportion CD4-, CD5-, and CD8-positive lymphocytes in BALF was not affected by administration of nHuIFNα. Oral administration of low-dose nHuIFNα reduced inflammation of the lower respiratory tract in Standardbred racehorses with IAD.