Several lines of evidence suggest that there may be compromises of immune responses
in humans or experimental animals exposed to weightless conditions during space
flight, or maintained in hypodynamic, hypokinetic, antiorthostatic models simulating
some aspects of weightlessness. Among those immune re- sponses and defenses
possibly altered in such conditions is the cytokine system. The present study
was carried out to determine the effects of a period of weight- lessness on
interferon (IFN) and interleukin-3 (IL-3) production by rats.
Spleens were removed from rats, separated into individual cells, suspended,
and supplemented with antibiotics. Cultures were then stimulated with concanavalin
A for 48 hours to induce IFN-gamma and IL-3. Supernatant fluids were har- vested
from the culture. Supernatant fluids were analyzed for IFN antiviral activity.
Due to cross reaction of rat and mouse IFN, the assay was carried out on mouse
L-929 cells using the Indiana strain of vesicular somatitis virus as the target.
Assays used were either a plaque reduction or microplaque reduction, and the
IFN titer corresponded to the reciprocal of the greatest dilution of the test
sample that reduced virus plaques by 50%. IL-3 assays were carried out by deter-
mining the ability of the supernatants to support the growth of an IL-3-dependent
cell line.
Spleens of all flown rats were substantially reduced in weight compared to con-
trols. Spleen cells of seven of ten ground control rats produced moderate levels
of IFN-g, while only one of ten flight rats whose IFN-g production was analyzed
produced any IFN-g, and the level of production of that one rat was at the lower
level of detection of the assay system. Decreased spleens size in flown rats
may be due to altered activity of T-lymphocytes in the spleen which are responsible
for IFN-y production. The drop in IFN-g production could been related to micro-
gravity, or to stress during postflight transport. However, it is unknown if
the IFN-g production decrease is permanent or transient in nature (i.e., would
IFN-g production have returned to normal had the rats been allowed to recover
further on the ground before sacrifice). Studies with antiorthostatic modeling
have suggested that, in mice, ability to produce IFN recovers after return to
normal caging. IL-3 production was not affected by space flight. Thus space
flight only affects specific components of the immune response.
Gould, C.L. et al.: Effects of Flight in Mission SL-3 on Interferon-Gamma Production
by Rats. Physiologist, supl., vol. 28, no. 6, 1985, pp. S213-S214.
Gould. C.L. et al.: Effects of Flight in Mission SL-3 on Interferon-Gamma Production
by Rats. Abstract S-213. Proceedings of the Seventh Annual Meeting on the IUPS
Commission on Gravitational Physiology, Niagara Falls, N.Y., October 13-18,
1985
Gould, C.L. et al.: Effects of Flight in Mission SL-3 on Interferon-Gamma Production
by Rats. Abstract 83.17. 36th Annual Fall Meeting of the American Physiological
Society, Buffalo, N.Y., October 13-18, 1985, Physiologist, vol. 28, no. 4, 1985,
p. 378
Gould, C.L. et al.: Inhibited Interferon-Gamma But Normal Interleukin-3 Production
from Rats Flown on the Space Shuttle. Aviation, Space, and Environmental Medicine,
vol. 58, no. 10, 1987, pp. 983-986.¥
Sonnenfeld, G. and E.S. Miller: The Role of Cytokines in Immune Changes Induced
by Spaceflight. Journal of Leukocyte Biology, vol. 54, no. 3, 1993, pp. 253-258.
Sonnenfeld, G. et al.: Effects of Antiorthostatic Suspension and Spaceflight
on Interferon Production and Immunity to Viruses. Space Life Science Symposium:
Three Decades of Life Science Research in Space, Washington, D.C., June 21-26,
1987, pp. 116-117.
Sonnenfeld, G. et al.: Inhibited Interferon Production after Spaceflight. Acta
Microbiologia Hungaria, vol. 35, no. 4, 1988, pp. 411-416.
¥ = publication of related ground-based study