Alveolar macrophage immaturity in infants and young children

Very little Is known about alveolar macrophage (AM) immunological function in early childhood. Using nonbronchoscopic bronchoalveolar lavage (BAL), th is study sought to compare the proportion, number, and function of AM betwe en very young and older children. BAL fluid (BALF) leukocyte parameters were determined in 63 children, and d ata divided into 3 age groups: group 1 (<2 yrs), group 2 (greater than or e qual to 2-less than or equal to 5 yrs) and group 3 (greater than or equal t o 6-less than or equal to 17 years). In a further subgroup of children, AM function and immune receptor expression were assessed, and data categorized into two age groups: <2 yrs and greater than or equal to 2 yrs of age. Compared to groups 2 and 3, the AM percentage in the BAL in group 1 was sig nificantly increased (median: 98% versus 92% and 91%), as was the albumin-a djusted AM concentration. AM from children <2 Srs expressed less human leuk ocyte antigen (HLA)-DR (versus <2 yrs of age), were less effective in reduc ing nitro blue tetrazolium, and released less interleukin (IL)-1 and tumour necrosis factor on Lipopolysaccharide stimulation. There was no difference in release of IL-6, expression of intercellular adhesion molecule-1 (CD54) , and AM stimulation of allogeneic T-cells, between children <2 yrs and gre ater than or equal to 2 yrs of age. It was concluded that the capacity of alveolar macrophage to stimulate T-ce lls is not enhanced in early childhood, and that immaturity of alveolar mac rophage function may contribute to an increased susceptibility to respirato ry infections in this age group.