PF4 and infection: Expression of immunological markers is also recorded 3 days after infection of C57BL/6 mice with PbA manifested as increased expression of PD-1 (programmed cell death protein) in the cerebellum, CTLA-4 (cytotoxic T lymphocyte associated with protein 4) and LAG-3 (lymphocyte activation gene 3: protein encoded by the LAG3 gene) in the hippocampus, as well as reduced expression of CXCL-4 in the hippocampus37.