In addition, patients with mutations in the extracellular domain of IL-7 receptor (IL7Rα or CD127) have severe combined immunodeficiency (SCID) of the T −B +NK + cells and suffer recurrent and severe respiratory bacterial and viral infections from the early infancy 7. Interleukin 7 (IL-7) plays a critical role in the homeostasis of the immune system, leading to the differentiation, proliferation, and survival of B, T, and natural killer (NK) cells 6. However, other factors could also be relevant. In CAP patients, it is hypothesized that depression of absolute peripheral blood T-cell counts represents the transfer of these cells towards the lung in order to be sequestered by protective mechanisms 5. Lymphocytopenia has been described in CAP, probably related to T-cells and T-cell subsets 5, and it has even been proposed as a predictive marker 4. The immune response is substantial in the control and recovery of the infection. A better understanding of the pathogenic factors is crucial to develop early biomarkers which could improve evaluation of severity risk at admission. However, these factors are not detected in some severe cases, and patients are wrongly classified 4. liver damage, cardiac insufficiency) are known risk factors which are included in clinical scores of severity such as the Pneumonia Severity Index (PSI) and CURB-65 1, 3. Some CAP patients need to be admitted to intensive care unit (ICU) (10–20%) 1, and some will die (5–10%) 2. In Chile, CAP is the seventh cause of death, particularly among the elderly 2. Increased plasmatic sIL7R could contribute to identifying adult CAP cases at risk of death.Ĭommunity-acquired pneumonia (CAP) is a frequent worldwide cause of death 1. A significant association between sIL7R levels and SNPs of the IL7R gene is described for the first time in adult CAP. In conclusion, rs3194051GG and rs987106TT IL7R genotypes were associated with a poorer prognosis. Plasma IL-7 levels were lower in ICU-admitted than in not ICU-admitted and in non-survivors than in survivors. The AUC of sIL7Rα levels predicting 30-day mortality was 0.71. rs6897932CC, rs987106AA and rs3194051GG carriers showed the highest while rs6897932TT showed the lowest sIL7Rα levels. sIL7Rα plasmatic levels were higher in non-survivors than in survivors, and in severe than in mild cases. CD3 +CD127 + lymphocytes were lower in severe than in mild cases in non-survivors than in survivors and in ICU than in non- ICU admitted cases. IL7Rα gene expression was lower in non-survivors than in survivors, and in severe than in mild cases. rs3194051GG was more frequent in non-survivors than in survivors rs987106TT was more frequent and rs3194051AA less frequent in patients at intensive care unit (ICU) than in those not admitted to ICU. The IL7Rα SNPs rs6897932, rs987106, and rs3194051 SNPs in IL7α were genotyped, the systemic expression of the IL7R gene, sIL7R, IL-7, and levels of peripheral IL7Rα + T lymphocytes were quantified in 202 hospitalized CAP cases. Since IL-7, membrane-bound receptor (IL7Rα CD127) and soluble IL7Rα (sIL7R) are critical in lymphocytes homeostasis, in this work we aimed to evaluate the involvement of the IL-7/IL7Rα axis in the severity of adult CAP, since it has not been explored. Lymphocytopenia has been frequently described in CAP. Recognized risk factors in some severe cases have not been identified. Community-acquired pneumonia (CAP) is a worldwide leading cause of death.