Macrophage inflammatory protein-1 alpha (not T helper type 2 cytokines) isassociated with severe forms of respiratory syncytial virus bronchiolitis

It has been suggested that the pathogenesis of respiratory syncytial virus (RSV) infection is related to the development of T helper (Th) type 2 cytok ine responses. The presence of Th1 and Th2 cytokines and the chemokines mac rophage inflammatory protein (MIP)-1 alpha and monocyte chemotactic protein (MCP)-1 were assessed by ELISA in nasopharyngeal secretions of infants wit h RSV infection. Infants with mild bronchiolitis had increased Th1 cytokine s and reduced Th2 cytokines, compared with infants with upper respiratory t ract illness alone. Severe bronchiolitis was characterized by a more balanc ed Th1-Th2 response that did not differ from that of infants with upper res piratory tract illness alone. In contrast, MIP-alpha was markedly increased in infants with severe bronchiolitis. MIP-1 alpha and MCP-1 levels also we re inversely related to oxygen saturation (P<.005). Thus, the severity of R SV bronchiolitis appears to be related more to chemokine release than to Th 2 cytokine production.