Serum KLRB1 (CD161) as a discriminative biomarker in community-acquired pneumonia.

AIMS: This study aimed to evaluate serum levels of killer cell lectin-like receptor B1 (KLRB1, CD161) as a biomarker for distinguishing between viral and bacterial causes in patients with community-acquired pneumonia (CAP). MATERIALS & METHODS: A total of 120 individuals were enrolled between November 2024 and January 2025: 46 with viral pneumonia, 44 with bacterial pneumonia, and 30 healthy controls. Serum KLRB1 levels were measured using ELISA. Microbiological cultures, PCR testing, and serology were used to classify pneumonia etiology. Additional laboratory and radiological data were collected. RESULTS: Streptococcus pneumoniae and Influenza A H1N1 were the most common agents for bacterial and viral pneumonia, respectively. KLRB1, CRP, and leukocyte levels were significantly higher in bacterial cases than viral ones (p < 0.001). KLRB1 levels were also significantly higher in healthy controls compared to both pneumonia groups. ROC analysis showed a KLRB1 cutoff of 5.11 ng/mL yielded 97% sensitivity and 85% specificity in distinguishing bacterial from viral pneumonia. CONCLUSIONS: Serum KLRB1 may serve as a valuable biomarker to differentiate between viral and bacterial CAP, supporting early diagnosis and optimized treatment decisions.