- Subjects with acute or chronic disease or who may be using drugs that might interfere with skeletal muscle metabolism / function or immune function will be excluded from participation. Other exclusion criteria include cognitive deficits identified by a Mini-Mental State Examination score < 24, mobility impairment requiring a wheelchair, infections, endocrine diseases (e.g., diabetes or untreated thyroid dysfunction), active inflammatory conditions, autoimmune disorders, renal dysfunction, anemia (hemoglobin < 11.5 g/dL), cardiac problems in preceding 3 months or congestive heart failure, chronic obstructive lung disease, neoplasia other than of the skin during the preceding 5 years, influenza vaccine within last 3 weeks or other vaccines within last 6 weeks, known systemic reaction to any immune function test antigen, and use of the following drugs: immunosuppressants, antianginal agents, antiarrhythmics, antibiotics within last 2 weeks, and oral steroids. Other conditions may be used as inclusion / exclusion criteria at the discretion of the study physician to ensure the safe participation of potential study subjects.