Dynamics of salivary immunoglobulin A and serum interleukin 6 levels in newborn calves

• Calves’ IL-6 production occurs directly after birth.
• IL-6 supports IgA production in saliva at specific time points.
• Salivary IgA appeared as early as two weeks after birth.

Mucosal immunoglobulin A (IgA) is an important component of the adaptive first line immune defense. Especially in newborn calves, where diarrheal pathogens can cause severe diseases, the adaptive mucosal immunity is crucial. Regulating local IgA production is complex. Cytokines and in particular, interleukin 6 (IL-6), are described to be main actors in this process. In vaccination trails, IL-6 is used to improve the immune response with ambiguous results. Therefore, this study investigated the influence of IL-6 on the physiological development of salivary IgA production in newborn calves. Ten clinically healthy female Holstein calves were sampled over a period of four weeks. Immunoglobulin A and IL-6 were measured in serum, colostrum, milk and saliva. In addition, to compare the mucosal immune response with the systemic immune response, immunoglobulin G was measured in serum, colostrum and milk, too, using a commercial enzyme-linked immunosorbent assay (ELISA). In order to determine the ability of newborn calves to produce IL-6 actively by themselves, the relative gene expression was analyzed in peripheral blood mononuclear cells (PBMC) using a quantitative reverse transcriptase polymerase chain reaction (qPCR). Interleukin 6 gene expression in PBMCs was detected directly after birth. A significant positive correlation between serum IL-6 and salivary IgA was found on day seven (p=0.043). Furthermore, the IL-6 serum concentration peaked on day 14 and coincided with a remarkable IgA increase in saliva (p<0.01). Therefore, IL-6 seemed to play a role during the first initialization phase of a local IgA response.