The neutrophil function and lymphocyte profile of milk from bovine mammary glands infected with Streptococcus dysgalactiae Maiara G Blagitz 1 *, Fernando N Souza 2 , Camila F Batista 1 , Luis Fernando F Azevedo 1 , Nilson Roberti Benites 3 , Priscilla Anne Melville 3 , Soraia A Diniz 2 , Marcos X Silva 2 , João Paulo A Haddad 2 , Marcos Bryan Heinnemann 3 , Mônica M O P Cerqueira 4 and Alice M M P Della Libera 1 1 Departamento de Clínica Médica, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, Av. Prof Dr Orlando Marques de Paiva, 87, Cidade Universitária, São Paulo 05508-270, Brazil 2 Departamento de Medicina Veterinária Preventiva, Escola de Veterinária, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 31270-010, Brazil 3 Departamento de Medicina Veterinária Preventiva e Saúde Animal, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, São Paulo 05508-270, Brazil 4 Departamento de Tecnologia e Inspeção de Produtos de Origem Animal, Escola de Veterinária, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 31270-010, Brazil Received 27 October 2014; accepted for publication 22 May 2015; first published online 29 June 2015 Streptococcus dysgalactiae is a bacterium that accounts for a notable proportion of both clinical and subclinical intramammary infections (IMIs). Thus, the present study explores the function of milk neutrophils and the lymphocyte profile in mammary glands naturally infected with Streptococcus dysgalactiae. Here, we used 32 culture-negative control quarters from eight clinically healthy dairy cows with low somatic cell counts and 13 S. dysgalactiae-infected quarters from six dairy cows. Using flow cytometry, we evaluated the percentage of milk monocytes/macrophages and neu- trophils, expression of CD62L, CD11b and CD44 by milk neutrophils, the levels of intracellular re- active oxygen species (ROS) production and phagocytosis of Staphylococcus aureus by milk neutrophils, and neutrophil viability. Furthermore, the percentages of B cell (CD21 + ) and T lympho- cyte subsets (CD3 + /CD4 + /CD8 - ; CD3 + /CD8 + /CD4 - ; and CD3 + /CD8 - /CD4 - ), and the expression of CD25 by T milk lymphocytes (CD3 + ) and T CD4 + milk cells were also assessed by flow cytometry using monoclonal antibodies. The present study showed a higher SCC and percentage of milk neu- trophils, and a decrease in the percentage of milk monocytes/macrophages from S. dysgalactiae- infected quarters when compared to uninfected ones. We also observed a higher expression of CD11b by milk neutrophils and a tendency toward a decrease in neutrophil apoptosis rate in S. dysgalactiae-infected quarters. In addition, the S. dysgalactiae-infected quarters had higher per- centages of milk T cells (CD3 + ) and their subset CD3 + CD8 + CD4 - cells. Overall, the present study provided new insights into S. dysgalactiae IMIs, including distinct lymphocyte profiles, and a tendency toward an inhibition of apoptosis in milk neutrophils. Keywords: Immune response, mastitis, somatic cell count, dairy cow. Mastitis is a disease of major economic importance, causing reduced milk production and quality and increasing the use of veterinary drugs worldwide. Several bacterial genera and species are capable of causing mastitis, and one of the most common groups of bacteria isolated from intramammary infections (IMIs) is Streptococcus spp., which includes Streptococcus dysgalactiae (Osteras et al. 2006; Whist et al. 2007; Souza et al. 2009; Zadoks & Fitzpatrick, 2009; Botrel et al. 2010; Schwarz et al. 2010; Beecher et al. 2012; Abrahmsén et al. 2014; Leelahapongsathon et al. 2014). For instance, Botrel et al. (2010) described that S. dysgalactiae was isolated in 8·8 and 9·4% of the milk samples from clinical and subclinical cases of mastitis, respectively. Mastitis organisms are categorised as contagious or envir- onmental pathogens based on their distinct characteristics of distribution and interaction with the teat and teat duct. *For correspondence; e-mail: magblagitz@uol.com.br Journal of Dairy Research (2015) 82 460–469. © Proprietors of Journal of Dairy Research 2015 doi:10.1017/S0022029915000308 460