Immunological attributes of blood and milk neutrophils isolated from crossbred cows during different physiological conditions

The goal of this work was to understand how polymorphonuclear leukocytes (PMN), the first line of cellular defence, integrate and prioritize multiple chemotactic signals to navigate during periods of demand like subclinical mastitis (SCM), clinical mastitis (CM), pregnancy (P), and calving (C). For this, blood and milk samples were collected from five groups of crossbred cows (healthy, with SCM, CM, pregnant, and newly calved). Maximum viability was seen in the PMN of healthy cows, whereas minimum viability was observed in CM cows. Phagocytic activity (PA) of blood and milk PMN decreased significantly (P < 0.05) at C and in CM cows. Chemotactic activity of blood PMN was minimum in C followed by CM, SCM, and P cows. PA was found to be negatively correlated with the plasma cortisol levels and inverse relationship was observed between the plasma interleukin-8 (IL-8) levels and the chemotactic activity of neutrophils. There was a significantly (P < 0.05) higher expression of CXCR1 and IL-8 on both blood and milk PMN of CM cows followed by C and SCM cows. Minimum expression of selectin (CD-62L) was seen on blood PMN isolated around calving, whereas maximum expression of integrin (CD-11b) was in CM cows. Healthy and P cows showed the highest expression of CD-62L on blood PMN but its expression remained unaltered in milk PMN. Irrespective of physiological stage of the cows, immune suppression was found to be always cortisol dependent. Observing the neutrophil activity and mRNA expression of genes isolated from cow neutrophils can be used as indicators to assess the health/ physiological status promptly for immediate therapeutic or management-related actions.