Immunologists and geneticists have figured out howeffective vitamin Ais absorbed by the immune cells of the intestinal microbiome, thereby improving adaptive immunity. The new findings could help treat digestive diseases. In addition, the study results provide new information about the effectiveness of some vaccines. Knowledge about the aspect of immune function could potentially manipulate how vitamin A should be delivered to the immune system as a therapy or as a prevention of disease.
How adaptive immunity can be built up with the help of vitamin A
According to the study authors, vitamin A is particularly important for the adaptive immune system. This is a subset of the broader immune system. It responds to certain pathogens that arise because of diseases or vaccines based on immunological memory. Although researchers knew that the so-called myeloid immune cells in the gut can convert retinol into retinoic acid, how they acquire it for this task was a mystery. The research team therefore investigated how resident gut bacteria influence the biology of humans and other mammals. The scientists focused on amyloid A proteins in the blood. This is a family of retinol-binding proteins that some organs produce during infections. They used biochemical techniques to determine which cell surface proteins they attach to and identified LDL receptor-related protein 1 (LRP1).
The study authors showed that LRP1 was present on myeloid cells in the intestine, where it appeared to secrete retinol. When researchers used genetic techniques to delete the gene for this receptor in mice and prevent their myeloid cells from absorbing the vitamin A derivative, the adaptive immune system in their gut disappeared. B cells as well as the molecule immunoglobulin A and critical components of adaptive immunity were significantly reduced. The researchers then compared the response to Salmonella infection between mice with LRP1 and those without. Those lacking the receptor were quickly overcome by the infection. The results suggest that LRP1 is the vehicle through which retinol enters myeloid cells. If researchers can find a way to inhibit this process, it could slow the immune response in inflammatory bowel disease and Crohn's disease. Alternatively, the findings could be fromthis studyprovide a way to increase immune activity, making oral vaccines, for example, more effective.
