Immune response in nonspecific mastitis: What can it tell us?

摘要

We analyzed a large number of immune responseparameters from quarter milk samples with distinctbacteriological and quarter somatic cell count (qSCC)statuses. Furthermore, we sought to explore and identifydisplayed immune response patterns in milk samplesfrom mammary glands with nonspecific mastitis. Thus,92 quarter milk samples from 28 cows were stratifiedinto 4 groups, as follows: (1) 49 culture-negative controlquarters with a low qSCC (<1 × 10~5 cells/mL)from 19 dairy cows (so-called healthy quarters); (2) 15culture-negative quarters with high qSCC (>2 × 10~5cells/mL; so-called quarters with nonspecific mastitis)from 10 dairy cows; (3) 8 culture-positive quarters withlow qSCC (noninflammatory quarters with low qSCC)from 5 dairy cows; and (4) 20 culture-positive quarterswith high qSCC (so-called truly infected quarters)from 8 dairy cows. Using flow cytometry, we evaluatedthe percentage of milk neutrophils and their viability,intracellular reactive oxygen species production, phagocytosis,and the expression of CD62L, CD11b, andCD44 for each of the 4 quarter strata. Furthermore, thepercentage of monocyte/macrophages, B cells, and Tlymphocyte subsets were evaluated by flow cytometry.Milk samples from bacteriologically negative quarters(both with a low and elevated qSCC) had a lower qSCCthan those with bacteriologically positive outcomes(both with a low and elevated qSCC). As expected,the healthy quarters showed the lowest percentage ofneutrophils and also showed a higher percentage ofmilk monocytes/macrophages and lower percentage ofT lymphocytes than truly infected quarters. The mostprominent result of the present study is that quarterswith nonspecific mastitis showed the highest percentageof milk CD4~+ T lymphocytes. The healthy quartershad a lower percentage of apoptotic neutrophils thannoninflammatory and truly infected quarters, althoughit did not differ from those from the quarters withnonspecific mastitis. Our study supports the role ofdifferential cell counting in the diagnosis of mastitis,as the milk leukocyte populations markedly fluctuateunder healthy and inflammatory conditions. Furthermore,an increase in milk CD4~+ T cells was associatedwith nonspecific mastitis, suggesting an increase in thisleukocyte subpopulation is correlated with low bacterialshedding. Our study allows us to go further in ourunderstanding of mammary gland immunity, providingfurther insights on potential protective mammary glandimmunity, which we hypothesize can open new avenuesfor the development of novel targets that can promotebovine udder health.