CCL2 and respiratory syncytial virus bronchiolitis: In humans, CCL2 levels correlate positively with disease severity: infants with RSV bronchiolitis who required mechanical ventilation show significantly elevated levels of CCL2 in BAL fluid compared with control infants intubated for non-infective causes22,23, and children with severe RSV disease displayed higher levels of CCL2 in nasopharyngeal wash samples than controls25.