Gene expression profile in zebu dairy cows (Bos taurus indicus) with mastitis caused by Streptococcus agalactiae

Abstract

Mastitis is an inflammatory response in the mammary gland caused by an influx of somatic cells, composed mainly of neutrophils, macrophages and lymphocytes. The speed and efficacy of the host’s immune response to the invasive pathogen affects the establishment, persistence and severity of the infection. To characterize the gene expression and response mechanism to infection by Streptococcus agalactiae (S. agalactiae) in zebu dairy cows of the Gyr breed, we carried out a transcriptome study of the cells present in the milk from 17 animals. Milk samples were collected before inoculation (hour 0) and 4, 9 and 24h after inoculation of the bacteria into one of the quarters and at 0 and 24h from one of the quarters not inoculated. The transcriptome analysis was done by the microarray and real-time PCR techniques. The microarray technique revealed the existence of 32 differentially expressed genes between inoculation and 4h afterward. The validation of these results by real-time PCR was done for eight genes. Besides these eight genes, the expression of six others was evaluated by real-time PCR even though they did not present a significant difference by the microarray technique. Of the 14 genes analyzed by real-time PCR, all showed a significant difference in expression for at least one of the comparisons between times. This analysis indicated an increase in the expression of all the genes that presented a significant difference in relation to hour 0, with most of them presenting maximum expression 24h after inoculation of the pathogen. Comparison of the gene expression between the inoculated and non-inoculated quarters showed greater expression in nine genes in the inoculated quarters. Analyses of gene networks revealed three modules with distinct characteristics 24h after inoculation and showed that some mechanisms are altered in Gyr dairy cows after infection of the mammary gland by S. agalactiae. In this study it was possible to verify changes in the expression of at least 14 genes related to the immune response of zebuine animals against intramammary infection caused by S. agalactiae. These genes can play important roles in fighting intramammary infection and maintaining the tissue during infection.