Objective To explore the significance of IL (interleukin)-1 receptor antagonist (IL-1ra) and radical S-adenosyl methionine domain-containing protein 2 (RSAD2) in pneumonia reaction.

Methods Fifty hospitalized patients with CAP were selected as the CAP group, and divided into a severe CAP group (n = 14) and a non-severe CAP group (n = 36) according to the 2007 adult CAP management guidelines of the Infectious Diseases Society of America/American Thoracic Society. Eighteen health examinees during the same period were selected as the control group. The levels of cytokine were measured using Bio-Plex Pro human cytokine screening plate. Spearman rank correlation method was used to analyze the correlation between the expression levels of plasma cytokine and CURB-65 scores. The prediction value of plasma cytokine levels in severe CAP patients was analyzed by the area under the ROC curve (AUC).

Results The age, length of hospital stay, and CURB-65 score of severe CAP patients were higher than those of non-severe CAP patients (P ＜ 0.05 to P ＜ 0.01). At admission, the levels of IL-1β, IL-1ra, IL-6, IL-13, IL-18, hepatocyte growth factor (HGF), RSAD2, monokine induced by interferon-γ (MIG), macrophage colony-stimulating factor (M-CSF), macrophage inflammatory protein 1β, and interferon-γ inducible protein 10 (IP-10) in the severe CAP group and non-severe CAP group were higher than those in the control group (P ＜ 0.05), and the levels of IP-10, IL-1ra, and M-CSF in the severe CAP group were higher than those in the non-severe CAP group (P ＜ 0.05); on the third and seventh day of the disease course, the levels of IP-10, HGF, MIG, and RSAD2 in the severe CAP group were higher than those in the non-severe CAP patients (P ＜ 0.05); on the third day of the disease course, the IL-18 level in the severe CAP group was higher than that in the non-severe CAP group (P ＜ 0.05); on the seventh day of the disease course, the IL-13 level in the severe CAP group was lower than that in the non-severe CAP group (P ＜ 0.05), and the IL-1β level was higher than that in the non-severe CAP group (P ＜ 0.05). ROC curve analysis showed that the top three cytokines in AUC were IL-1ra (0.930), IP-10 (0.866), and RSAD2 (0.803); the AUC of the combination of IL-1ra and RSAD2 was 0.990, AUC of the combination of IP-10 and IL-1ra eas 0.976, AUC of the combination of RSAD2 and IP-10 was 0.857, and AUC of the combination of three cytokines was 0.990. Spearman rank correlation analysis showed that at admission, the expression levels of IP-10, RSAD2, HGF, MIG, and IL-1ra were significantly positively correlated with CURB-65 scores (r_s = 0.651, 0.580, 0.632, 0.513, 0.473, P ＜ 0.01).

Conclusions IL-1ra and RSAD2 are highly correlated with the severity of CAP, and can be used as good predictors of severe CAP. Therefore, detecting the expression levels of IL-1ra and RSAD2 in patients with early CAP can provide useful information for formulating specific treatment strategies.