Expression of CD45 isoforms in normal human CNS and in HIV‐1 encephalitis

Abstract

CD45 is a membrane tyrosine phosphatase that modulates the development and function of hematopoietic cells including macrophages. Several isoforms of CD45 exist as a result of alternative splicing of the extracellular domain exons (A, B and C). Agonist antibodies to CD45 isoforms have been shown to suppress microglial activation, proliferation and HIV infection, suggesting its potential as a new therapeutic target. To determine the cell‐type and disease‐specific expression of CD45 isoforms in human CNS, sections of HIV‐1 encephalitis (HIVE) and controls (HIV‐ and HIV+) were studied by immunohistochemistry using CD45 exon‐specific (RA, RB, RC and RO) antibodies. The results showed that RA and RC expression was limited to rare lymphocytes, while RB expression was robust in microglia (both control and HIVE) and inflammatory cells (T cells and macrophages). RO was low in control microglia, but increased in HIVE. T cells and macrophages also expressed RO. Our study demonstrated that CD45 expression in the CNS is limited to two isoforms (RB and RO) and that RB is also expressed in resting ramified microglia. Targeting CD45RO with an antibody might be a therapeutic option for neuroinflammatory diseases.