Different manufacturers use several different processes for the production of intravenous immunoglobulin.
Several manufacturers include a production step where the immunoglobulin is treated with low levels of pepsin
at pH 4. A series of experiments were undertaken to assess whether or not pH 4/pepsin treatment could inactivate a
range of test viruses. Acid-labile viruses such as vaccinia, herpes simplex, mumps and Semliki Forest virus were
found to be susceptible to pH 4/pepsin treatment whereas poliovirus type 2, an acid-stable virus, was completely
resistant to this treatment. In immunoglobulin preparations, viral contaminants are likely to be present as antibody/
virus complexes and such complexing was found to help protect the test viruses from inactivation by pH 4/pepsin
treatment. Despite this protection, at least 99% of the test inoculum of two susceptible viruses (vaccinia and herpes
simplex) was found to be inactivated after treatment and the subsequent dissociation of virus/antibody complexes. It
is concluded that pH 4/pepsin treatment may contribute to the safety of intravenous IgG by inactivating potential
viral contaminants.