The Determination of TH1/TH2 Cytokine Balance in Milk According to the Bacterial Species that Cause to Subclinical Mastitis in Cows

This thesis study aimed to determine the Th1/Th2 cytokine balance in milk according to the bacterial species (Escherichia coli, Streptococcus agalactiae, and Staphylococcus aureus) which causes subclinical mastitis in cows. One hundred and eighty cows were included in the study. California Mastitis Test (CMT) was performed on the cows. In the CMT, cows with negative four quarters were included in the CMT (-) group (n = 45). Escherichia coli group (n = 45) was designated as cows with only Escherichia coli growing in milk samples of CMT-positive, Streptococcus agalactiae group (n = 45) as cows with only Streptococcus agalactiae growing in milk samples of CMT-positive, and Staphylococcus aureus group (n = 45) as cows with only Staphylococcus aureus growing in milk samples of CMT-positive. Somatic cell counts (SCC) in milk samples were measured by using a Cell Counter device. Milk composition analysis was performed using the Laktoscan device, and cytokine analysis was performed using species-specific commercial ELISA kits. In the Escherichia coli group, while milk TNF-α and IFN-γ levels were found high, IL-2 levels were found low. The lowest milk IL-4 level was found in the CMT (-) group. While the highest milk IL-5 level was found in the Streptococcus agalactiae group, the highest milk IL-10 level was detected in the Staphylococcus aureus group. Also, increased somatic cell count (SCC) in milk caused a decrease in TNF-α and IFN-γ levels and an increase in IL-5 levels. However, it was determined that IL-2, IL-4, and IL-10 levels were not affected by the SCC change. Moreover, while the percentage of fat in the milk samples was found the highest in the Escherichia coli group, the percentage of solid-not-fat, protein, lactose, and mineral matter was found the lowest. As a result, it was determined that the Th1/Th2 polarization balance shifted towards the Th1 direction in the Escherichia coli group. The Th1/Th2 polarization balance was found to be in the Th2 direction in the Streptococcus agalactiae and Staphylococcus aureus groups. According to our findings, it was concluded that cellular immunity should be kept strong in mastitis cases due to Escherichia coli, and humoral immunity should be supported in mastitis caused by Staphylococcus aureus and Streptococcus agalactiae.