FOXP3 and respiratory syncytial virus bronchiolitis: Levels of circulating FOXP3 mRNA and the counts of FOXP3+ CD4+ regulatory T cells, which encompass both suppressive resting Treg cells (CD45RA+ FOXP3lo) and suppressive activated Treg cells (CD45RA+ FOXP3hi), are diminished in infants who are hospitalized due to RSV bronchiolitis.