The incidence of nosocomial pneumonia (NP) among injured patients is substantial. We hypothesize that traumatic injury induces alterations in local organ effector cell function that may predispose the lungs of injured patients to infection. It is the objective of this study to compare the systemic and alveolar effector cell response to injury and assess the relationship these have to the development of NP. Peripheral blood and bronchoalveolar lavage fluid (BAL) were collected from 10 elective surgery patients (controls) and 16 multitrauma patients at 12, 36, and 60 h post-injury. Systemic and alveolar levels of IL-8 and IL-10 were measured. CD11b expression on peripheral blood neutrophils (PBN) and alveolar neutrophils (AN) and HLA-DR expression on peripheral blood monocytes (PBM) and alveolar macrophages (AM) were measured. Alveolar levels of IL-8 and IL-10 were significantly higher than systemic levels after injury. HLA-DR expression was reduced on both PBM and AM after injury but was lowest on the AM. Six of 16 patients (38%) developed NP (NP+). There were no differences in cytokine levels (IL-8 and IL-10) or effector cell phenotype (CD11b and HLA-DR expression) within the systemic circulation of NP+ and NP- patients. In contrast, NP+ and NP- patients differed significantly in alveolar cytokine levels and alveolar effector cell phenotype. IL-8 was significantly higher in BAL form NP+ patients at all time points after injury. Furthermore, alveolar levels of IL-10 decreased in NP- patients but increased in NP+ patients. In all patients, AM HLA-DR expression was significantly reduced from normal controls 12 h post-injury. In NP-patients, AM HLA-DR expression returned to normal 60 h post-injury, whereas in NP+ patients, expression remained suppressed. These findings identify distinct trends in local organ cytokine production and alterations in effector cell phenotype that precede NP. The persistence of reduced HLA-DR expression amidst increasing levels of IL-10 in NP+ patients suggest that cell-mediated immune function is being suppressed. As such, local organ immunosuppression may be responsible for the development of nosocomial pneumonia in injured patients.