Arabinogalactans are starch-like chemicals found in many plants.They are proteoglycans (a type of protein and sugar combination) found between the cells. It is very plentiful in Larch trees. There are a number of studies that show it to be beneficial to the immune system. The activity of immune modulating herbs, like Echinacea and Astragalus, may be due to arabinogalactan.
A study, appearing in Current Medical Research and Opinion (2013 Mar;29(3):251-8), found that 4.5 grams of Larch arabinogalactan per day over a 12-week period reduced the incidence of the common cold in 101 subjects when compared to 98 subjects receiving a placebo.
Other research, appearing in Nutrition and Metabolism (2016 Apr 12;13:28) reviewed studies involving Larch arabinogalactan and the immune system the authors stated, ” Larch arabinogalactan decreased the incidence of cold episodes by 23 %. Improvements of serum antigen-specific IgG and IgE response to Streptococcus pneumoniae and tetanus vaccination suggesting a B cell dependent mechanism have been reported in vaccination studies with larch arabinogalactan, while the absence of response following influenza vaccination suggests the involvement of a T cell dependent mechanism. These observations suggest a role for larch arabinogalactan in the improvement of cold infections, although the mode of action remains to be further explored. Different hypotheses can be envisaged as larch arabinogalactan can possibly act indirectly through microbiota-dependent mechanisms and/or have a direct effect on the immune system via the gut-associated lymphoid tissue (GALT).”