Jarrow Formulas Larix 1000 contains arabinogalactans extracted from the larch tree (Larix occidentalis). Arabinogalactans are densely branched, high molecular weight, water-soluble polysaccharides that support healthy immune function, particularly macrophage activity and cytokine defense activity such as interferon gamma, tumor necrosis factor, IL-1 and IL-6. Arabinogalactans also promote the growth of the probiotic bacteria Lactobacilli and bifidobacteria.