C-Reactive Protein (CRP) Enhances Murine Antibody-Mediated Transfusion Related Acute Lung Injury (TRALI)

Transfusion-related acute lung injury (TRALI), a syndrome characterized by respiratory distress triggered by blood transfusions, is the leading cause of transfusion-related mortality. Mostly, TRALI has been attributed to passive infusion of human leucocyte antigen (HLA) and human neutrophil antigen (HNA) antibodies present in the transfused blood product. Several animal models have been developed to study the pathogenesis of antibody-mediated TRALI and various mechanisms for TRALI induction have been suggested, including involvement of endothelial cells, neutrophils and monocytes. In 2006, a murine of model of antibody-mediated TRALI was developed using a monoclonal MHC class I antibody (clone 34-1-2s). This antibody was shown to cause significant lung damage (excess lung water: pulmonary edema) within 2 hours of administration into BALB/c mice, which in follow-up studies was only reproducible after initial priming with the gram-negative endotoxin lipopolysaccharide (LPS). 34-1-2s was also shown to cause severe lung damage in severe combined immunodeficient (SCID) mice. We investigated 34-1-2s mediated TRALI in BALB/c mice, without LPS priming, and found no difference in TRALI severity when compared with injection with an control isotype antibody for 34-1-2s (Isotype Mouse IgG2a antibody), as examined by lung wet-to-dry ratios, a measure for pulmonary edema. Recently it was described that the acute phase protein C-reactive protein (CRP), heavily up-regulated during acute infections and also present at lower levels in healthy individuals, was able to enhance antibody-mediated platelet destruction both in vitro and in vivo via Fc-receptor mediated phagocytic responses. Considering the fact that TRALI has been shown to be mainly antibody-mediated, plus the fact that it has been suggested to be an Fc-dependent process as well, we investigated the effect of CRP in a murine antibody-mediated TRALI. We tested if CRP would be able to enhance antibody-mediated TRALI in the murine 34-1-2s based BALB/c TRALI model. For that purpose, we co-injected CRP together with 34-1-2s and compared that to co-injection of CRP together with control isotype mouse IgG2a or to injection with CRP alone. We found that CRP+34-1-2s injection resulted in significantly higher lung damage than CRP+isotype antibody, as well as than CRP alone, with at least 43% of the mice in the CRP+34-1-2s group having a lung wet-to-dry ratio of higher than 5, which is considered to represent severe lung damage. As the monocyte-derived neutrophil chemoattractant macrophage inflammatory protein 2 (MIP-2: murine equivalent of human IL-8) was recently shown to play a central role in murine (SCID) 34-1-2s-mediated TRALI induction, we measured MIP-2 values in our BALB/c TRALI model and found that CRP alone was capable of producing high levels of MIP-2, which were found to be even more increased when 34-1-2s was co-injected with CRP. We propose a mechanism in which CRP plays a synergistic role with 34-1-2s antibody to significantly increase the induction of antibody-mediated TRALI via enhanced stimulation of monocyte-derived MIP-2 secretion.