ICOSLG and viral encephalitis: As shown in Fig. 2, the serum of patients with LGI1 encephalitis had reduced levels of CD28, ICOS-L, PDCD1 (all p < 0.05), and CD86 (p < 0.01), but higher levels of ICOS (p < 0.05) and PD-L2 (p < 0.001) were detected.