The biological functions of complexes containing the RhD protein are unknown. However, they might be involved in NH3 /NH4+ detoxification of organs. Ammonia, the product of protein catabolism is extremely toxic, especially for brain cells and must be quickly removed from the sensitive organs. It was observed that the concentration of ammonium is three times higher in red cells than in plasma and it was further suggested that the RhD containing complex plays a key role in its capturing and its transport to the kidneys and the liver. It was also suggested that the complex might participate in intracellular pH regulation and consequently also in the regulation of local oxygen tension. It was suggested that RhD-negativity-associated anoxia in certain parts of the nervous system could be responsible for physiological (and also behavioral) effects of the RhD phenotype. The variation of the oxygen tension in various organs and tissues could, of course, influence also other biological functions, including the functions of the immune system. This could explain why RhD negativity seems to be associated with neurological, mental health and immunological disorders. The probable roles of the RhD-containing complex in keeping the normal morphology and adhesiveness of red cells could be responsible for the observed associations of RhD negativity with some haematological and inflammation-related diseases, including arthritis.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0141362
https://www.datebytype.com/blogs/view/115/Ammonia-smell-when-sick