Final answer:
The 17-year-old female likely has Common Variable Immunodeficiency, indicated by low immunoglobulin levels but normal B cell counts, leading to increased risk of infections, especially in the respiratory and gastrointestinal tracts.
Step-by-step explanation:
A 17-year-old female with decreased levels of IgG, IgM, IgE, and IgA yet possessing a normal number of B cells likely has a diagnosis of Common Variable Immunodeficiency (CVID). This condition typically manifests with a decreased production of multiple immunoglobulin classes despite normal B cell numbers. The differential diagnosis could include agammaglobulinemia, but this condition typically presents with very low to absent B cells.
The main complication associated with CVID, and similar immunodeficiencies, is an increased susceptibility to infections, particularly of the respiratory and gastrointestinal tracts. Since secretory IgA plays a critical role in mucosal immunity, its deficiency can lead to recurrent lung and gastrointestinal infections. The causal pathogens may include H. influenzae, S. pneumoniae, Moraxella catarrhalis, S. aureus, Giardia lamblia, or pathogenic Escherichia coli.