CD8+ T cell count and its subtypes were independent factors associated with 28-day mortality of ARDS caused by A. baumannii pneumonia (CD8+ T cell count: OR 3.667, 95% CI 1.553–8.659, P = 0.003; CD8+CD28+ T cell count: OR 2.043, 95% CI 1.871–31.801, P = 0.005; CD8+CD38+ T cell count: OR 2.705, 95% CI 1.152–6.353, P = 0.022) (Table 4). The gene discussed is CD28; the disease is acute respiratory distress syndrome.