T-T cell crosstalk: Insights into mechanisms and disease development 2254071

Introduction Intercellular signaling is essential for immune coordination and cellular identity. While interactions between innate and adaptive immune cells are established, the mechanisms driving direct T—T cell communication are poorly understood. We hypothesized that CD4 memory T cells (CD4 Tmem) can directly interact with naïve CD8 T cells (CD8 TN) to influence their activation state, and we tested this both ex vivo and in vivo. Methods We identified the phenotype by performing ex vivo co-culture of human CD4 memory T cells (CD4 Tmem) with naïve CD8 T cells (CD8 TN) and assessing surface marker expression (CD45RO, CCR7). To test in vivo relevance, OVA-specific CD8 TN (OT-I) were co-adoptively transferred with OVA-expressing CD4 Tmem into wild-type B6 mice, and activation was measured by surface marker expression. Mechanistic signaling was evaluated using both CD8 TN and CD4 Tmem cells from NR4A-GFP reporter mice, where GFP expression serves as a reporter of NR4A activity downstream of TCR signaling. To assess disease relevance, we developed an ex vivo model using ApoE⁻/⁻ aorta co-cultured with T cells. Results Ex vivo, CD4 Tmem induced an activated-memory phenotype in CD8 TN. In vivo, co-transferred OT-I cells showed activation and differentiation, whereas OT-I cells injected alone did not. CD8 TN co-cultured with activated CD4 Tmem upregulated CD44 and NR4A-GFP, indicating TCR engagement. In the atherosclerosis model, co-cultured CD8 TN and CD4 Tmem cells induced Annexin V+ apoptosis in CD45⁻ aortic cells, whereas CD8 TN alone did not. Conclusion These results highlight a CD4-driven mechanism that activates naïve CD8 T cells and promotes vascular pathology.