Effect over time of in-vivo administration of the polysaccharide arabinogalactan on immune and hemopoietic cell lineages in murine spleen and bone marrow

Current evidence indicates an immunostimulating role for complex carbohydrates, i.e., polysaccharides, from several plant sources. In the present work, we determined the specific in vivo effects, with time of administration, of one such compound, a neutral arabinogalactan from larch not only on immune (lymphoid) cells, but also on natural killer (NK) lymphoid cells, as well as a variety of other hemopoietic cells in both the bone marrow and spleen of healthy, young adult mice. The latter were injected daily (i.p.) with arabinogalactan (500 microg in 0.1 ml pH 7.2 phosphate buffered saline-PBS) for 7 or 14 days. Additional, aged (1 1/2-2 yr) mice were similarly injected for 14 days only. Control mice were given the PBS vehicle in all cases, following the above injection regimen. Animals from all groups were sampled 24 h after the final injection and the immune and hemopoietic cell populations in the bone marow and spleen were assessed quantitatively. The results indicated that immediately following either 7 or 14 days of arabinogalactan administration to young, adult mice, lymphoid cells in the bone marrow were significantly decreased (p < 0.004; p < 0.001, respectively) relative to controls but remained unchanged at both time intervals in the spleen. NK cells, after 7 days of arabinogalactan exposure, were also decreased significantly in the bone marrow (p < 0.02), but unchanged in the spleen. After 14 days' exposure to the polysaccharide, NK cells in the bone marrow had returned to normal (control) levels, but were increased in the spleen (p < 0.004) to levels greater than 2-fold that of control. Among other hemopoietic cell lineages, none was influenced in the bone marrow or spleen by one-week administration of arabinogalactan; however, after two-week exposure, precursor myeloid cells and their mature (functional) progeny (granulocytes), were significantly reduced in the spleen (p < 0.043; p < 0.006, respectively), as were splenic monocytes (p < 0.001). These lineages in the bone marrow, however, remained steadfastly unaltered even after 14 days of continuous exposure to the agent. Of the vast cascade of cytokines induced in the presence of this polysaccharide, it appears that immunopoiesis- and hemopoiesis-inhibiting ones are most prevalent during at least the first two weeks of daily exposure.