C4A and hyperinsulinemic hypoglycemia, familial, 4: CXCR5+CD4+ Tfh cells are specialized cells that provide help to B cells especially during affinity maturation which is essential for high-affinity antibody production and the development of memory B cells [28] Laboratory measured immune abnormalities reported in the literature include elevated levels of IgG, IgA, IgM, and IgE, deficiency of the complement component C1q, and low C3 and C4 complement levels [13, 14, 26, 29].