Defective B-cell memory in patients with Down syndrome

Area of Science:

• Immunology
• Genetics
• Pediatrics

Background:

• Patients with Down syndrome exhibit immunologic defects, increasing risks for autoimmune diseases, malignancies, and infections.
• Low circulating B cell counts suggest compromised humoral immunity in Down syndrome.

Purpose of the Study:

• To investigate immunodeficiency in Down syndrome by examining B-cell compartment defects.
• To understand the specific B-cell subset alterations contributing to immune dysfunction.

Main Methods:

• Analyzed blood B-cell subset composition, replication history, somatic hypermutation, and class-switch recombination in 17 children with Down syndrome.
• Examined germinal centers and plasma cells in tonsils from 4 additional children with Down syndrome.

Main Results:

• Reduced naive mature and memory B cells observed, despite normal transitional B cells and elevated B cell-activating factor.
• Normal germinal centers, plasma cells, and serum immunoglobulin levels were found.
• Impaired proliferation and somatic hypermutation in natural effector B cells; normal in memory B cells. IgA and IgM memory B cells showed defective antigen selection.

Conclusions:

• While germinal center and plasma cell formation appear normal, reduced memory B cells and impaired IgA/IgM maturation in Down syndrome are significant.
• Defects in circulating IgA and IgM B-cell memory may underlie impaired mucosal immunity.
• These B-cell defects likely contribute to the heightened susceptibility to respiratory tract infections in individuals with Down syndrome.