Isolation and analysis of lymphocytes. (i) Isolation of mononuclear cells from
the spleen and CNS. Spleens were harvested from mice either at 5 or 7 days
postinfection. Spleen cell suspensions were prepared by gently homogenizing
spleens in a nylon bag (mesh opening, 64 m) with a syringe plunger in RPMI
1640 medium supplemented with 1% fetal calf serum. Then, red blood cells were
lysed with 0.83% NH4Cl. Mononuclear cells were prepared from the CNS as
previously described by Phillips et al. (25) on day 7 after i.c. inoculation. Three
(mesh opening, 64 m).
Percoll (Pharmacia) was added to a final concentration of 30%, and the lysate
was centrifuged at 1,300 g for 30 min at 4°C. The cell pellet was resuspended,
passed through a cell strainer (pore diameter, 70 m; Becton Dickinson), and
washed. The cells were then layered over 2 ml of Lympholyte-M (Cedarlane
Laboratories) and centrifuged at 1,300 g for 20 min at room temperature. Cells
were removed from the interface, washed once, and counted.