CD19 and viral infectious disease: The T follicular helper (Tfh) cell and germinal center B (GC B) responses, critical for long-term protection against virus infection, were also assessed using flow cytometry.34,35 We observed elevated frequencies of Tfh (CD4+CXCR5+PD-1+) cells and GC B (CD19+GL7+CD95+) cells in inguinal lymph nodes (Fig. 3d, f) and spleen tissues (Fig. 3e, g), following immunization with the RBDXBB.1.5-HR vaccine, suggesting that our monovalent vaccine may confer long-term protective immunity.