The Secretome of Female CD8+ T‐cells Increases Monocyte Phagocytosis
Authors: Pippin Sarah , Troncoso Miguel , DeLeon-Pennell Kristine Y. 
Published: April 2020

Cardiovascular diseases including myocardial infarction (MI) are the leading cause of death in the US. Elevated CD8+ T‐cell counts (>1065 cells/mm3) have been linked to increased mortality rate (2‐fold) in post‐MI patients. In a previous study conducted by our lab, we concluded that CD8+ T‐cells regulate macrophage recruitment and impair collagen deposition during the early phase post‐MI, leading to adverse cardiac remodeling and decreased survival. Interestingly, survival was improved in male but not female mice lacking functional CD8+ T‐cells (p<0.05) compared to WT animals from the respective sex. Based on these data, we hypothesized in the current study that CD8+ T‐cells have detrimental effects in males during the post‐MI remodeling process through cellular communications with macrophages. In order to address this hypothesis, we employed C57Bl/6J mice (WT; n=3/sex), and mice with non‐functional CD8+ T‐cells (CD8atm1mak; n=3/sex). The animals underwent permanent occlusion of the left anterior descending coronary artery to induce the MI, and macrophage activation and tissue necrosis was evaluated by immunoblotting and flow cytometry at post‐MI day 3. Male CD8atm1mak mice have more necrotic myocytes within the day 3 infarct compared to CD8atm1mak female mice and WT animals of either sex. Protein assessment of macrophage phagocytosis maker, Mertk, revealed that WT females had lower Mertk shedding compared to both WT males and CD8atm1mak female mice, indicating that Mertk‐mediated phagocytosis is higher in WT females than the other groups. To determine if the secretion profile of CD8+ T‐cells was regulating macrophage physiology, we isolated CD8+ T‐cells from the spleens of male and female WT mice and cultured them in RPMI supplemented with 1% antibiotics and 10% FBS (positive control) or 0.1% FBS (unstimulated, negative control). To test influence of effector and memory CD8 T‐cells, cells were stimulated in vitro for 24 hours towards a memory phenotype (1.5 ng/mL IL4) or effector phenotype (1 ng/mL IL12), and secretome was collected from all groups. The collected secretome was used to stimulate bone marrow monocytes isolated from female mice (2‐hour stimulations). Bone marrow monocytes stimulated with the secretome from female effector CD8+ T‐cells had increased phagocytosis mirroring what was observed in vivo. In conclusion, CD8 T‐cells in females but not males correlated with decreased shedding of Mertk and increased macrophage‐mediated removal of necrotic debris. Our data suggests that this may be due to sex differences in the effector phenotype post‐MI.Support or Funding InformationThis work was supported by the Biomedical Laboratory Research and Development Service of the Veterans Affairs Office of Research and Development Award IK2BX003922 and the National Institutes of Health award number U54DA016511. This work was also financially supported, in part, by the 2019 S&R Foundation Ryuji Ueno Award that was bestowed to Dr. DeLeon‐Pennell by the American Physiological Society. This work was also supported by the Ralph H. Johnson VA Medical Center. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health, the Veterans Administration, or the American Physiological Society.