IVIG is used for three purposes;
[I]   for patients who do not make antibodies or gammaglobulin
[II]  for patients with specific infections, and
[III] for patients with autoimmune and inflammatory diseases. 

Some individuals make no or too few antibodies and thus suffer from recurrent infections. Sometimes the antibody producing cells (B-cells) of individuals have an intrinsic inability to make antibodies; these are patients with Primary Immunodeficiency diseases, and many require life-long IVIG infusions.

Examples include X-linked Agammaglobulinemia and Common Variable Immunodeficiency.
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