Community-acquired pneumonia occurs when the immune system is unable to mount a homeostatic, balanced response against a respiratory pathogen, which subsequently results in an infection. Although weakened immunity is considered important for the pathogenesis of communityacquired pneumonia, to date, the potential clinical applications of immunological profiling have not been extensively studied. Nonetheless, increasing evidence suggests that evaluation of a patient’s immune response could help to improve severity assessment and prognosis prediction in this disease (figure). Lymphocytes are a crucial component of pulmonary immunity. In a previous study, 1 we found that the presence of lymphopenia confers an increased risk of mortality in patients who are admitted to hospital with communityacquired pneumonia (known as lymphopenic community-acquired pneumonia). Addition of lymphocyte count to the CURB-65 score for pneumonia severity improved the ability to predict 30-day mortality. 1 Lymphocyte count is obtained from the leukogram, which is an easily available and inexpensive test. Humoral immunity (ie, immunoglobulins and the complement system) is essential for the prevention and response to respiratory infection. Defects in humoral immunity, such as common variable immunodeficiency, are associated with increased risk of pulmonary infections due to encapsulated bacteria. Generally, available vaccines prevent pneumonia via the generation of antibodies. In patients who are admitted to hospital with community-acquired pneumonia, low IgG2 concentrations in serum are an independent marker of intensive care unit (ICU) admission and mortality. 2