Analysis of plasma surfactant protein D levels in lung transplant recipients

In lung transplant recipients (LTRs), severe clinical complications, such as microbial infections of the lung or transplant rejection, may occur. Surfactant protein D (SP-D) is a C-type lectin that is mainly produced in alveolar type II cells. Plasma SP-D levels are usually low, but may increase when the lung-blood barrier is impaired. In this study, we analyzed whether plasma SP-D concentrations reflect rejection or infection of the lung allograft. An enzyme-linked immunosorbent assay was used to measure SP-D levels in plasma samples from 58 LTRs during intervals without pathologic respiratory findings and during episodes of acute cellular rejection (ACR), microbial colonization, and microbial pneumonia. Median plasma SP-D levels were significantly increased during episodes of microbial pneumonia, but not in the absence of pathologic respiratory findings, during microbial colonization, or during ACR up to grade A2-A3 (P < 0.05). During pneumonia, an increased plasma SP-D level was detected in 60% of LTRs and this was further associated with a significantly higher risk for the patients to develop stage III bronchiolitis obliterans syndrome (BOS III) or to die within the subsequent 6 months after pneumonia (P = 0.0093). All patients with a plasma SP-D level of >300 ng/mL during pneumonia developed BOS III and/or died within 6 months of follow-up (P = 0.001). The determination of SP-D levels in plasma during pneumonia in LTRs may be of prognostic value and warrants further evaluation.