MAG and infection: To confirm that infection did not alter the number of mature or immature OLs and to determine whether OL from infected mice exhibited changes to the expression of myelin proteins, flow cytometry was performed on events isolated from entire brains of PBS- and IAV-inoculated mice at day 8 p.i. The cell isolation procedure generated three distinct populations of events: myelin debris (defined as SOX10−PLP+ or SOX10−MAG+ events), immature OLs (defined as SOX10+PLP− or SOX10+MAG−) and mature OLs (defined as SOX10+PLP+ or SOX10+MAG+).