Using the logistic regression model, no effect on the expression of CTLA-4 and PD-1 by T-cells was observed on: (1) occurrence of IMIs by any pathogen (including all pathogens); (2) occurrence of IMIs by major mastitis pathogens only; or on (3) new IMIs by any pathogen (including all pathogens). Here, PDCD1 is linked to mastitis.