B-cell defects constitute the majority of primary immunodeficiencies (approximately 50-70% of PIDD). B-cell PIDD are a heterogeneous group of diseases that are characterized by:
- reduction or absence of immunoglobulins, e.g. IgG, IgM, IgA
- reduction or absence of specific antimicrobial antibodies. e.g. IgG against pneumococcus (specific antibody deficiency with normal immunoglobulin levels, SADNI)
Primary immunodeficiency disorders (PIDD) (click to enlarge the image).
Substitution of immunoglobulin G (IgG) is the mainstay of treatment of B-cell PIDD.
While from the late 1970s, the intravenous route of administration (IVIG) was the most common, in the past decades, subcutaneous immunoglobulin replacement therapy (SCIG) has become more popular.
Dosage and IgG trough level remain subjects of debate.
Higher IgG trough levels seem to improve the protection against recurrent infections and thus better prevent complications such as bronchiectasis.
Some patients, however, achieve protection with IgG trough levels on the lower IgG limit of healthy persons. Therefore, an individual protective IgG trough level needs to be defined for each patient.
Use of prophylactic antibiotics and immunosuppressive drugs differs among centres and requires future investigation.
Stem cell transplantation
Haematopoietic stem cell transplantation (HSCT) has been used as curative treatment in certain patients with B-cell defects associated with cell deficiencies, for example in two class-switch recombination defects and in selected severe forms of common variable immunodeficiency (CVID).
Which PIDD is most common?
Antibody (50%), T cell defects (20%), phagocyte def (20%), Complement (2%). Mnemonic: 50-20-20-2.
Modern management of primary B-cell immunodeficiencies. Hoernes M, Seger R, Reichenbach J. Pediatr Allergy Immunol. 2011 Dec;22(8):758-69. doi: 10.1111/j.1399-3038.2011.01236.x.