The proportions of CD4+ and CD8+ T cells expressing either CTLA-4 or PD-1 were similar in the two mouse strains during the first 6 days of infection, but surprisingly, on day 7 – i.e. at exactly the time when susceptible mice began to show signs of ECM – the proportions of both CD4+ and CD8+ T cells expressing CTLA-4 and PD-1 were significantly higher in ECM-susceptible C75BL/6 mice than in ECM-resistant BALB/c mice (Figure 2A, B). Here, PDCD1 is linked to infection.