IgG2 antibodies are used predominantly against bacteria with capsule polysaccharides (S. pneumonia, H. influenzae), and while the role of IgG4 is still being studied, decreased levels can be associated with IgA deficiency (along with IgG2 deficiency) and a Th-1 activation in Lyme borreliosis, while elevated levels have been associated with systemic fibro-inflammatory disorders of unknown origin [231]. This evidence concerns the gene NELFCD and selective IgA deficiency disease.