Blood samples were analyzed by measuring total blood proteins and plasma protein fractions involved with the immune system. Protein concentrations and electrophoretic patterns were evaluated to study humoral immunity. Cellular immunity function was evaluated by lymphocyte response to in vitro mitogenic challenge with phytohemagglutinin (PHA). Lymphocytes were tested for DNA and RNA synthesis rates. The RNA synthesis rate after 24 hours in culture, and the DNA synthesis rate after 72 hours in culture, were determined from 3H-uridine and 3H-thymidine uptake, respectively. The higher the uptake of 3H-uridine and 3H-thymidine indicated a positive response to the PHA mitogen. In addition, on Skylab 4, T-lymphocyte counts, B-lymphocyte counts, and the mixed lymphocyte test were conducted, prompted by findings from Skylab 2 and Skylab 3. Furthermore, lymphocytes from Skylab 4 astronauts were examined by electron microscopy to study cell membrane characteristics.
The plasma protein profiles after Skylab 2 indicated that (1) no significant changes were observed in total proteins and electrophoretic patterns (2) no significant changes were observed for immunoglobulins (3) no significant changes were observed for protease inhibitors (4) a slight decrease in complement component, C3, was observed immediately post flight in all three crewmembers was, by 13 days post flight, within the normal levels and (5) post flight two crewmembers had increased levels of lysozyme that were elevated for 13 days. In addition, there were no significant plasma protein modifications during Skylab 3 or Skylab 4.
Lymphocyte responsiveness was decreased in most Skylab astronauts on the day of recovery. However, this finding, characteristic of all three missions, did not appear to be related to the duration of the flight. Lymphocyte responsiveness recovered rapidly, and by 3 to 7 days post flight was within the established preflight limits. These changes prompted further studies conducted on Skylab 4 to observe the response of cells in a mixed lymphocyte culture and to quantitate preflight and post flight B- and T- lymphocyte distribution. It was found that the lymphocyte responsiveness was decreased temporarily on Skylab 4. However, lymphocyte function tested by the mixed lymphocyte reaction indicated that lymphocyte function was normal on landing day. The number of circulating T-cells on recovery day was decreased, but returned to normal levels by post flight day 3. In contrast, a transient elevation in the number of B-cells were observed on post flight day 1, with a rapid return to normal levels by post flight day 3. It was believed that hormones might be the cause for the temporary alterations of the mechanisms of lymphocyte functions. Absolute white cell count was elevated at recovery, but returned to preflight levels. Differential counts indicated that this elevation was due to an increase in the number of neutrophils without significant change in lymphocyte counts.