Relationship of CM to CCR5 expression on leukocytes and a radio-resistant brain cell. CCR5 expression on leukocytes and a radio-resistant cell in the brain is essential for CM. (A) Histograms of CCR5 expression on peripheral blood mononuclear cells of WT mice engrafted with WT BM, KO mice engrafted with KO BM, WT mice engrafted with KO BM, and KO mice engrafted with WT BM. Expression of CCR5 was assessed on peripheral blood leukocytes 10 weeks after BM engraftment for all reconstituted mice (7 to 10 per group). These histograms are representative of one mouse per group. Control is shown as a thin line. (B-C) CM incidence occurring between day 7 and day 13 (B) and survival time (C) of WT mice engrafted with WT BM (n = 8), KO mice engrafted with KO BM (n = 8), WT mice engrafted with KO BM (n = 10), and KO mice engrafted with WT BM (n = 8) and all infected with PbA (10⁶ PE) 10 weeks after reconstitution. Neurologic signs first appear late on days 7 to 10, with death occurring 2 to 3 days after their onset (shaded area). On day 13, as calculated by Fisher exact test, P < .05 between WT mice engrafted with WT BM and KO mice engrafted with KO BM.