IL33 and central nervous system cancer: Furthermore, using differential expression of CD45 on CD11b+ cells to distinguish between resident microglia (i.e., CD45low), activated microglia (i.e., CD45intermediate), and cerebral infiltrating leukocytes (i.e., CD45high) a significant increase in activated microglia was seen in the IL-33+ vs. IL-33− 1492 syngeneic glioma, and this increase was associated with a decrease in the number of resting (homeostatic) microglia.