In this study, irrespective of HPV type and HIV status, significant positive correlations were observed between CD4/CD28 and CD4/CD25 in stroma and between CD25/CD28 in stroma and epithelium of SIL specimens, indicating that CD4 cells are activated, i.e., expressing co-stimulatory molecule (CD28) and responding to IL-2 by expressing CD25. This evidence concerns the gene CD28 and squamous cell intraepithelial neoplasia.