2015 ACVIM Forum Research Abstract Program

This data may aid in the development of an effective vaccine and strategic vaccination protocols for Lyme disease in horses. Pneumonia is the most common cause of morbidity and mortality in foals <6 months of age. In contrast, pulmonary immunocompeteny in adult horses appears more robust given resistance to the same diseases that cause clinical manifestations in foals. We speculated that there would be quantitative and qualitative differences in the cell populations recovered in bronchoalveolar lavage fluid (BALF) that could provide insight into the progressive age-related gain in immunocompetency. Serial BALF was collected from a cohort of healthy foals at 1 week; 1, 2, 6, 12 and 18 months of age. BALF from foals was then compared to BALF collected from healthy adult horses. Cellular morphologic evaluation and 300 cell differentials were performed on cytocentrifuged BALF samples. Foals had significantly higher percentages of macrophages than adult horses at 1 week, 1 month, 2 months, and 6 months of age; this difference was no longer noted at 12 months of age. Foals had significantly lower percentages of lymphocytes in BALF than adult horses (week 1, months 1, 2, and 6). Furthermore, foals had a significantly higher percentage of macrophages compared with adults, characterized by a progressive increase in percentage of macrophages concurrent with an increase in age. To better define potential qualitative differences in pulmonary-alveolar macrophages (PAMs) between adult horses and foals, a longitudinal analysis of reactive intermediate activity between adult and foal PAMs was performed with samples from a subset of foals (n = 3) at age 1 week, 1, 6 and 12 months. In vitro measurements of superoxide and peroxynitrite were obtained using oxidation of dihydroethidium (DHE) and dihydrorhodamine (DHR) as indicators, respectively. PAMs were gated and sorted as live cells expressing CD172a, seeded in triplicate into 96-well plates, and allowed to adhere for 2 hours. PAMs were then stimulated with LPS (2 lg/mL) + IFNc (10 ng/mL); opsonized zymosan (0.5 mg/mL) or R. equi antigen (75 lg/mL) and incubated at 37°C for 30 hours. DHE or DHR was added 30 minutes prior to fluorimetry (BMG Labtech FluoStar Omega). For all stimulants, we documented an age-related progressive increase in production of superoxide and peroxynitrite with foals exhibiting lower levels of reactive intermediates at week 1 compared to month 12 (P < 0.05). Taken together, these results reveal a decreasing shift in percentage of PAMs in BALF as foals age along with a concurrent age-related increase in reactive intermediate production by PAMs. These results support the notion that the pulmonary cell population changes as foals age, with a large percentage of macrophages having decreased capacity for reactive intermediate production early in life. Collectively, these findings are consistent with age-related susceptibility of foals to pneumonia caused by the macrophage-tropic bacterium, R. equi. Corynebacterium pseudotuberculosis biovar equi infection in horses, also called pigeon fever, has not been reported in Alabama. Our previous studies had surprisingly identified positive synergistic hemolysis inhibition (SHI) titers in a number of healthy horses. The purpose of this study was to investigate the seroprevalence of C. pseudotuberculosis in this non-endemic population; and to determine the association of detectable titers with exposure to small ruminants with or without history o