Activation status of peripheral blood leucocytes in Leishmania chagasi naturally infected dogs categorized according to their clinical status as asymptomatic (AD = ), oligosymptomatic (OD = ) and symptomatic (SD = ▪) dogs. Uninfected dogs were used as a control group (CD = □). The results are expressed as average of major histocompatibility complex (MHC)-II expression reported as mean fluorescence channel (MFC) and CD45RB/CD45RA expression index plus standard deviation. Significant differences at P < 0·05 are indicated by the letters ‘a’, ‘b’, ‘c’ and ‘d’ in comparison to CD, AD, OD and SD, respectively. Representative histograms illustrating the higher MHC-II expression on circulating lymphocytes from AD are also presented.