CTLA4 and infection: When assessed for correlation with their corresponding clinical parameters, patients sampled on day 1 of admission who later developed culture-positive infection had elevated frequency of CTLA4+CD4+ T cell, which correlated positively with Model for End-Stage Liver Disease score (r = 0.675, P = .01) (Figure 2E) and ammonia (r = 0.771, P = .07) (Table 1).