Primary selective immunoglobulin (Ig) M deficiency usually presents early in life with recurrent or severe infections caused by encapsulated and gram-negative organisms. Primary selective IgM deficiency in adults is rare and is usually associated with autoimmune diseases or malignant neoplasm. We performed an extensive immunological analysis of innate and adaptive immunity in an adult patient with possible
primary selective IgM deficiency who presented with life-threatening Streptococcus pneumoniae septic shock and invasive Aspergillus fumigatus infection. The patient had no evidence of autoimmune disease or malignant neoplasm. Serum IgG, IgA, and IgE were normal; however, serum IgM levels and specific antibody titers against all 14 pneumococcal polysaccharide serotypes were consistently low. Complement
CH50, C3, C4, and neutrophil phagocytosis and oxidative burst were normal. Toll-like receptor expression on monocytes was also normal.
Therefore, adult patients with serious life-threatening and unusual infections should be investigated for possible selective primary IgM deficiency.

Key words: Selective IgM deficiency. Primary immunodeficiency. Unusual infections. Toll-like receptors. Autoantibodies. Aspergillosis. Complement. Immune complexes.