CD4 and systemic lupus erythematosus: In SLE patients carrying the STAT4 risk allele rs7574865[T], T cells exhibit increased STAT4 protein and pSTAT4 lever, and elevated IFN-γ production after PHA/interleukin (IL)-2 activation, whereas in healthy individuals, STAT4 risk allele carriers have reduced pSTAT4 levels in CD8+ and CD4+ T cells (89).