Impaired upregulation of CD86 on naive B cells in response to stimulation has been reported in a subset of CVID patients [166,167], a disease thought to be genetically related to SIgAD on the basis of the co-occurence of both disorders in the same families [3,33,36,168,169], the similarity in underlying immune dysfunction, the progression of SIgAD to CVID [170], and evidence of shared genetic associations [41,168]. Here, CD86 is linked to selective IgA deficiency disease.