Regulatory T cells are present predominantly in spleen and lymph nodes, but at a low frequency also in the brain Two week old mice were intracerebrally (i.c.) infected with 10 3 PFU recombinant MV expressing the rodent brain-adapted haemagglutinin CAMH and eGFP, or, when indicated, the recombinant MV without eGFP. Both recombinant viruses (rMV Edtag EGFP-CAMH and rMV Edtag CAMH) have the same distinct tropism for mouse neurons, and infections cause similar acute and persistent CNS infections [24, 33, 34, 35] . These recombinant viruses were designated throughout the manuscript as rMV-green and rMV.