The characteristics of immune factors in somatic cells from lactating dairy cows and their association with commensal bacteria in normal milk have not been clarified. This study investigated the relationship between the pathogenic bacteria in milk and somatic cell immune factors in healthy lactating cows.
Material and Methods
In total 44 healthy Holstein cows were studied on one farm. Milk samples were collected aseptically using a cannula and these samples were cultured for detection of bacteria and analysis of mRNA of immune factors expressed by somatic cells. Cows were divided into two groups based on the microbial status of their milk samples: 12 cows showed bacteria in cultures (positive group), and the other 32 cows did not (negative group).
The mRNA levels of IL-6, lactotransferrin, and cathelicidin expressed by somatic cells after milking decreased significantly compared to those before milking in both groups (P < 0.05). There were significantly lower mRNA levels of IL-6 and cathelicidin in the positive group compared to those in the negative group before milking.
These results suggest that mRNA levels of IL-6 and cathelicidin expressed by the somatic cells may be affected by the presence of bacteria in healthy lactating dairy cows.
The expressions of cytokines mRNA, including interleukin-4 (IL-4), interleukin- 17A (IL-17A) and interferon-gamma (IFN-γ), their master regulatory transcription factors, and signal transducers and activator of transcription (STAT) stimulated in vitro with Pasteurella (P.) multocida soluble antigen were examined in peripheral blood mononuclear cells (PBMC) from Holstein calves. The healthy Holstein calves were divided into three groups; 2 weeks old (2W Group, N=8), 6 weeks old (6W Group, N=8), and 10 weeks old (10W Group, N=8). PBMC were stimulated in vitro by soluble antigen of P. multocida. There were significantly lower expressions of IFN-γ, IL-4, and STAT-6 mRNA of PBMC stimulated with P. multocida soluble antigen in the 2W Group compared to that in the 10W Group. Expression of IL-17A and IFN-γ in PBMC stimulated with P. multocida soluble antigen were significantly higher compared with the PBMC without stimulation in the 6W groups. The results of the present study demonstrated that 2W old calves had decreased cytokine expression of PBMC when in vitro stimulated with P. multocida soluble antigen in vitro.