In Bare Lymphocyte Syndrome, failure of antigen presentation is due to defective expression of

Ans. a (MHC class I genes) (Ref. Nelson Textbook of Pediatrics 17th / 699; Robbin's pathology 7th/pg. 244)BARE LYMPHOCYTE SYNDROME# It is a condition caused by deficiencies in major histocompatibility complex:- Type 1: MHC class I (HLA-A, -B, and -C) antigens- Type 2: MHC class II (HLA-DR, -DQ, and -DP) antigens# Isolated deficiency of MHC class I antigens, the bare lymphocyte syndrome, is rare.- The resulting immunodeficiency is much milder than in SCID, contributing to a later age of presentation. - Sera from affected children contain normal quantities of MHC class I antigens and ss2 -microglobulin.- But MHC class I antigens are not detected on any cells in the body.- There is a deficiency of CD8 but not CD4 T cells.# The bare lymphocyte syndrome, type II (MHC class II is not expressed).- The result is that the immune system is severely compromised.- Clinically, this is known as a severe combined immunodeficiency (SCID).- MHC class II-deficient patients have a very low number of CD4 T cells but normal or elevated numbers of CD8 T cells. Lymphopenia is only moderate. The MHC class II antigens HLA-DP, DQ, and DR are undetectable on blood B cells and monocytes, even though B cells are present in normal number.# Rx: Bone marrow transplant is currently the only treatment.IMMUNODEFICIENCY DISEASESPhagocytic DeficienciesHumoral DeficienciesCell-mediated Combined immunodeficiences# Reduced neutrophils# Defective phagocytes# Adherence defects# Chemotactic defects# Killing defects# X-linked agammaglobu- linemia# X-linked hyper-IgM syndrome# Common variable hypo- gammaglobulinemia# Selective immunoglobulin deficiencies# DiGeorge syndrome# Reticular dysgenesis# Bare lymphocyte syndrome# SCID# Wiskott-Aldrich syndrome# Complement deficiencies