By monitoring the response to immunization and the inflammatory reaction to the intramammary challenge, we found that milk leukocytosis correlated strongly with antigen-specific production of IL-17A and IFN-γ upon re-stimulation of the whole blood of the sensitized cows, and that this cytokine production was dependent on CD4+ T lymphocytes. This evidence concerns the gene IL17A and Increased total leukocyte count.