CD4+ T cells dominate the leukocyte infiltration response initiated by intra-dermal injection of phytohemagglutinin into growing feathers in chickens

Phytohemagglutinin (PHA) is commonly used to evaluate cell-mediated immunocompetence. In chickens, PHA is typically injected intra-dermally (i.d.) into the skin (e.g., wing web, wattle, or footpad), and the tissue swelling response is monitored, whereby the extent of tissue swelling positively relates to the individual’s cell-mediated immune system capabilities. Although i.d. injected PHA was shown to stimulate mononuclear cell and basophil infiltration to the site of injection, reports on temporal, qualitative, and quantitative aspects of the local cutaneous PHA response are limited. The objective of this study was to use the growing feather (GF) as a cutaneous test site to assess and monitor the type and relative amounts of leukocytes present in the pulp of PHA-injected GF. For this study, male, non-vaccinated Light-brown Leghorn chickens reared at the Arkansas Experiment Station Poultry Health Laboratory were used. At 9 wk of age, the dermis of 20 18-day-old regenerating GF was injected with 10 μL of either PBS diluent or 300 μg/mL PHA-P (5 chickens per treatment). GF were collected from each chicken before (zero) and at 0.25, 1, 2, 3, 4, 5, and 7 d post injection. At each time point, one GF was collected for immunofluorescent staining of pulp cell suspensions and leukocyte population analysis by flow cytometry, and another GF for histological analysis. Histological analysis confirmed participation of granulocytes and mononuclear cells, primarily lymphocytes, in the cutaneous PHA response. As revealed by flow cytometric cell population analysis, T cells, especially CD4+ T cells, constituted the major portion of the mononuclear cell infiltrate. Levels of CD4+ T cells were greatly elevated in PHA-injected GF within 6 h and remained elevated throughout the 7-day examination period. γδ T cells, CD8+ T cells, and B cells also infiltrated in response to PHA although at lower levels and with different time-course patterns from CD4+ T cells. The dominant presence of CD4+ T cells at the site of PHA injection further affirms this polyclonal response as an indicator of cell-mediated immunity.