This study seeks to define the role of CD4+ and CD8+ T cell memory responses in the immunologic failure of patients with cystic fibrosis (CF) to clear infections. In a normal host, the immune system clears pathogens upon re-infection more swiftly and efficiently than during an initial infection, in great part due to the recall and effector functions of memory T cells. In CF, far less is understood regarding the response of T cell memory when hosts reencounter antigens, otherwise known as pulmonary exacerbations. Pulmonary exacerbations are pivotal events that lead to a decline in health status among CF patients, with many never recovering to baseline health. CF patients will be recruited from patients followed by the Adult CF Program at National Jewish Health. Following enrollment at the time of antibiotic initiation, blood will be collected at two different time points. The first samples will be collected within 24 hours of starting IV antibiotic therapy. The second blood specimen will be collected at the end of hospitalization, after a minimum of 5 days. At the time of each blood draw, complete blood counts, a sputum sample, and simple spirometry will be measured as part of the standard care of a CF exacerbation. Isolated PBMCs will be stained with antibodies to designate cell surface phenotype. They will then be sorted to identify the T cell population. These cells will be tested on their ability to clear pathogens. The relationship between cellular immune responses and clinical indicators of pulmonary status will be examined by fitting linear mixed models.

Inclusion Criteria:

• Documented diagnosis of CF.
• Age 18 years old or greater.
• Hospitalization with planned IV antibiotic treatment for a pulmonary exacerbation of CF.
• Ability to perform reproducible Pulmonary Function Tests and produce sputum.
• Willingness to comply with study procedure and willingness to provide written consent.

Exclusion Criteria:

• Presence of a condition or abnormality that, in the opinion of the Principal Investigator (PI), would compromise the safety of the patient or the quality of the data.
• Use of systemic steroids at the start of IV treatment for a pulmonary exacerbation

Adult CF subjects will be recruited from patients followed by the Adult CF Program at National Jewish Health at the onset of an acute pulmonary exacerbation.