Characterization of antibodies to capsular polysaccharide antigens of Haemophilus influenzae type b and Streptococcus pneumoniae in human immune globulin intravenous preparations

Abstract

The most common infections in primary immune deficiency disease (PIDD) patients involve encapsulated bacteria, mainly Haemophilus influenzae type b (Hib) and Streptococcus pneumoniae (pneumococcus). Thus, it is important to know the titers of Hib- and pneumococcus-specific antibodies that are present in immune globulin (Ig) intravenous (IGIV) preparations used to treat PIDD. In this study, seven IGIV preparations were tested by enzyme-linked immunosorbent assay and opsonophagocytic activity for antibody titers to the capsular polysaccharides of Hib and five pneumococcal serotypes. Differences in Hib- and pneumococcus-specific antibody titer were observed among various IGIV preparations, with some products having higher- or lower-than-average titers. Opsonic activity also varied among preparations. As expected, IgG2 was the most active subclass of both binding and opsonic activity except against pneumococcal serotype 6B where IgG3 was the most active. This study determines antibody titers against capsular polysaccharides of Hib and pneumococcus in seven IGIV products that have been shown to be effective in reducing infections in PIDD patients. As donor antibody levels and manufacturing methods continue to change, it may prove useful from a regulatory point of view to reassess IGIV products periodically, to ensure that products maintain antibody levels that are important for the health of IGIV recipients.

FIG. 1.

Anti-Hib concentrations in IGIV products. Seven licensed IGIV products (five lots each) were tested for anti-Hib antibody concentrations, indicated as micrograms of specific antibody per milligram of total IgG, by ELISA. Each point on the graph represents an IGIV lot, and the mean anti-Hib concentration is represented by a horizontal solid line. The mean anti-Hib concentration of all the products is represented by the dashed line across the graph, while the dotted lines above and below indicate 1 standard deviation (0.23 ± 0.05 μg/mg of IgG).

FIG. 2.

Anti-Hib IgG subclass concentrations. Three IGIV products, B, C, and G, were selected for analysis, and IgG subclasses were separated with a protein A column and FPLC. Anti-Hib IgG subclass levels were measured with an ELISA.

FIG. 3.

Summary of antipneumococcal concentrations. The means of the antipneumococcal serotype concentrations of all lots were calculated and are summarized in a bar graph. Each bar is the mean of five IGIV lots of the same product. The error bars indicate standard deviations.

FIG. 4.

Antibody concentrations to pneumococcal serotypes 4, 6B, 9V, 14, and 19F (panels A to E, respectively). Antibodies to pneumococcal serotypes were measured for the same IGIV lots as in Fig. 3A. The mean antiserotype concentration for all the lots is indicated by the dashed middle line, whereas the standard deviation is indicated by the dashed lines above and below the mean. The solid line indicates the mean concentration within the same product.