This condition is caused due to a defective T-cell signaling resulting in failure to produce IgG in the body. This occurs in persons between the ages of 13 and 35 years. In this condi-tion, the number of B cells is normal, but the ability to pro-duce IgG and other immunoglobulins is greatly reduced. The cell-mediated immunity is normal. Patients with this condition are highly susceptible to infections caused by S. pneumoniae, H. influenzae, and other pyogenic bacteria. Administration ofintravenous gamma globulin reduces the infections caused by these bacteria.
In malnutrition, the synthesis of IgG is reduced due to low sup-ply of amino acids. People with malnutrition, hence, are sus-ceptible to infection by pyogenic bacteria.