Immune dysfunction in hypophosphatemic vitamin D-resistant rickets: Immunoregulatory reaction of 1α(OH) vitamin D₃

We investigated immunologic function in six cases with hypophosphatemic vitamin D-resistant rickets (VDRR) before and after treatment with 1α-hydroxycholecalciferol (1α(OH) vitamin D₃). All cases suffered frequent episodes of infection, which tended to be more severe in the older patients. OKT9-, OKT10-, and OKM1-positive cells and adenosine deaminase (ADA) were significantly increased, whereas numbers and activity of natural killer (NK) cells were lower than normal before treatment. After administration of 1α(OH) vitamin D₃, however, the susceptibility to infection apparently decreased, and NK cell number and activity increased in all patients. ADA was also significantly decreased and remained in the normal range after treatment. These results suggest that vitamin D plays a role in the impaired immunoregulatory functions of NK cells in VDRR. Furthermore, ADA may be one parameter reflecting this immunologic impairment.