CD28 and systemic lupus erythematosus: No difference in % or absolute CD8+ T cell counts in SLE vs. HC or in absolute CD8+CD28+ or CD8+CD28− T cell counts.Decreased % CD28− of CD8+ T cells in SLE vs. HC (p < 0.01). Increased % CD28+ of CD8+ T cells in SLE vs. HC (p < 0.01).