The most frequent Caucasian MHC haplotype, AH8.1 - associated with numerous immunopathological differences and certain autoimmune diseases - was recently linked to the delayed onset of bacterial colonization in cystic fibrosis. Based on this observation, we hypothesized that the carriers of AH8.1 have lower risk for a worse outcome in sepsis. AH8.1 carrier state was determined in 207 Caucasian patients with severe, pneumonia-related sepsis. Our data showed that in patients without chronic obstructive pulmonary disease (COPD), septic shock - a serious consequence of the bacterial infection - occurred significantly less frequently (OR=0.3383; 95% CI=0.1141-0.995; p=0.043) in carriers of AH8.1, than in non-carriers. According to the multivariate logistic regression analysis, this haplotype had an independent protective role against septic shock in all patients (OR=0.315; 95% CI=0.100-0.992; p=0.048), particularly in COPD-free patients (OR=0.117; 95% CI=0.025-0.554; p=0.007). These results indicate that AH8.1 may confer protection against the progression of bacterial infection, and this could explain, at least partially, its high frequency in the Caucasian population.
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