RT Journal Article T1 Immunological composition of human milk before and during subclinical and clinical mastitis A1 Castro Navarro, Irma A1 Pace, Ryan M. A1 Williams, Janet E. A1 Pace, Christina D. W. A1 Kaur, Harpreet A1 Piaskowski, Julia A1 Aragón, Alberto A1 Rodríguez Gómez, Juan Miguel A1 McGuire, Mark A. A1 Fernández Álvarez, Leonides A1 McGuire, Michelle K. AB Mastitis, an inflammatory condition affecting more than 25% of breastfeeding women, is usually associated with reduced milk secretion, pain, and discomfort, which often leads to early cessation of breastfeeding. Although the etiology of mastitis is multifactorial, a pro-inflammatory state of the mammary gland might be a risk factor. However, changes in milk composition, and specifically in the milk immune profile, prior to and during mastitis have not been well described. To help close this research gap, we documented the immune profiles of milk produced by both breasts of 10 women experiencing clinical (CM) and 8 women experiencing subclinical (SCM) mastitis during the week of sign/symptom development as well as the week prior and compared them with milk produced by 14 healthy controls. CM was defined as having signs/symptoms of mastitis, whereas SCM was presumed if the participant did not have signs/symptoms of CM, but her milk had a somatic cell count >400,000 cell/mL and/or sodium-to-potassium (Na/K) ratio >1.0. Concentration of 36 immune factors (including immunoglobulins, cytokines, chemokines, and growth factors) was quantified via immunoassays. Milk produced by women who developed CM had distinct immune profiles the week prior to diagnosis, particularly elevated concentrations of pro-inflammatory cytokine IL-1b and regulatory cytokines IL-2, IL-4 and IL-10. In contrast, immune profiles in milk produced by women with SCM did not differ from that produced by healthy women or those with CM the week prior to mastitis onset. Once mastitis appeared, marked changes in milk’s immune profile were observed in both CM and SCM groups. CM was characterized by elevated concentrations of 27 compounds, including proinflammatory cytokines (IL-1b, IL-1ra, and TNFa) and chemokines (including IL-8, eotaxin, IP-10, MCP-1, MIP1a, and MIP1b), compared to healthy controls. Milk’s immune profile during SCM was intermediate, showing higher levels of IL-6, IFNg, and MCP-1 compared to healthy controls, suggesting a milder, more controlledimmune response compared to CM. Only milk produced by the mastitis-affected breast had altered immune profiles. Further research is needed to determine if these differences in milk’s immune profiles can be used to improve mastitis risk prediction prior to onset of symptoms. PB Frontiers Media YR 2025 FD 2025 LK https://hdl.handle.net/20.500.14352/118258 UL https://hdl.handle.net/20.500.14352/118258 LA eng NO Castro-Navarro, I., Pace, R. M., Williams, J. E., Pace, C. D. W., Kaur, H., Piaskowski, J., Aragón, A., Rodríguez, J. M., McGuire, M. A., Fernandez, L., & McGuire, M. K. (2025). Immunological composition of human milk before and during subclinical and clinical mastitis. Frontiers in immunology, 15, 1532432. https://doi.org/10.3389/fimmu.2024.1532432 NO IC: Formal analysis, Investigation, Visualization, Writing – original draft. RP: Data curation, Formal analysis, Investigation, Writing – review & editing. JW: Conceptualization, Data curation, Formal analysis, Funding acquisition, Supervision, Writing – review & editing. CP: Data curation, Formal analysis, Writing – review & editing. HK: Formal analysis, Writing – review & editing. JP: Formal analysis, Writing – review & editing. AA: Investigation, Writing – review & editing. JR: Resources, Supervision, Writing – review & editing. MAM: Conceptualization, Funding acquisition, Project administration, Supervision, Writing – review & editing. LF: Resources, Supervision, Writing – review & editing. MKM: Conceptualization, Funding acquisition, Project administration, Supervision, Writing – review & editing NO National Institutes of Health (NICHD) NO US Department of Agriculture National Institute of Food and Agriculture (USA) NO Idaho Agricultural Experiment Station (USA) NO National Institute of General Medical Sciences (USA) DS Docta Complutense RD 7 abr 2025