Interestingly, CX3CR1 (fractalkine receptor) was present on the vast majority of CD4+CD28null T cells (HC: 88.2 ± 3.9%; MS: 82.4 ± 4.7%; RA: 90.4 ± 1.5%) and mostly absent on CD4+CD28+ T cells (HC: 2.6 ± 0.9%; MS: 1.5 ± 0.6%; RA: 2.4 ± 0.5%).