Opsonic and physicochemical characteristics of intravenous immunoglobulin preparations

Measuring quantity and function of pneumococcal antibodies in immunoglobulin products

BACKGROUND

Immunoglobulin replacement therapy is a cornerstone of the treatment of primary immunodeficiencies. Preparations used for replacement therapy are processed by purifying immunoglobulins from large pools of plasma, which were obtained from healthy donors. The constituent antibodies in these products depend on the immune history of the donor pool as well as manufacturing processes that differ among manufacturers. For these reasons various methods have been proposed to examine the levels and function of antibodies to organisms such as Streptococcus pneumoniae, which frequently causes infections in patients with immunodeficiencies. Pneumococcal antibody levels or antibody function can be measured with enzyme-linked immunosorbent assay (ELISA) or multiplexed opsonophagocytosis assay (MOPA). Although these assays were developed initially to assess the immunogenicity of pneumococcal vaccines, the techniques have been adapted to evaluate immunoglobulin products as well.

STUDY DESIGN AND METHODS

This article provides a concise review of the analytic techniques for measuring pneumococcal antibodies and prior studies of immunoglobulin products utilizing these methods.

RESULTS

Studies utilizing these assays have demonstrated that antibody levels of immunoglobulin products can vary with time, location, and manufacturer.

CONCLUSIONS

We highlight current issues and future considerations concerning measurement of pneumococcal antibodies in immunoglobulin products, and the assays used for this purpose.

Monomeric and dimeric IgG fractions show differential reactivity against pathogen-derived antigens

Polyvalent Ig preparations, derived from the pooled plasma of thousands of healthy donors, contain a complex mix of both 'acquired' and natural antibodies directed against pathogens as well as foreign and self/auto antigens (Ag). Depending on their formulation, donor pool size, etc., liquid Ig preparations contain monomeric and dimeric IgG. The dimeric IgG fraction is thought to represent mainly idiotype-antiidiotype Ab pairs. Treatment of all IgG fractions at pH 4 effectively monomerizes the IgG dimers resulting in separated idiotype-antiidiotype Ab pairs and thus in a comparable F(ab')(2) binding site availability of the different IgG fractions. Previously, we identified an increased anti-self-reactivity within the monomerized dimer fraction. This study addressed if, among the different IgG fractions, an analogous preferential reactivity was evident in the response against different pathogen-derived protein and carbohydrate antigens. Therefore, we assessed the activity of total unseparated IgG, the monomeric and dimeric IgG fractions against antigenic structures of bacterial and viral antigens/virulence factors. All fractions showed similar reactivity to protein antigens except for exotoxin A of Pseudomonas aeruginosa, where the dimeric fraction, especially when monomerized, showed a marked increase in reactivity. This suggests that the production of antiidiotypic IgG antibodies contributes to controlling the immune response to certain categories of pathogens. In contrast, the monomeric IgG fractions showed increased reactivity towards pathogen-associated polysaccharides, classically regarded as T-independent antigens. Taken together, the differential reactivity of the IgG fractions seems to indicate a preferential segregation of antibody reactivities according to the nature of the antigen.

Differences between IGIV products: impact on clinical outcome

The use of immune globulin intravenous (IGIV) as replacement therapy in immunodeficiency disease and as anti-inflammatory or immunomodulatory therapy in a variety of autoimmune and inflammatory diseases has expanded dramatically over the last decade. With this expansion, new challenges and concerns have emerged. As well, new products have been introduced while others have been discontinued. This evolution poses the important issue of product selection, choosing the "right" product for an individual patient. As the manufacturing process, virus reduction methods, and final formulation and composition differ widely among these products, it is intuitive that clinical outcomes, including both safety and efficacy, could also differ. This review examines such differences among currently available products in the United States and their potential to affect clinical outcomes.

Treatment of autoimmune mucocutaneous blistering diseases with intravenous immunoglobulin therapy

Autoimmune mucocutaneous blistering diseases (AMBDs) are a group of rare diseases that affect the skin and mucous membranes and are potentially fatal. They have variable clinical presentation, course and prognosis. Their immunopathology is well-characterised and target antigens have been studied. Many patients respond to conventional therapy, which consists of high-dose long-term systemic corticosteroids with an immunosuppressive agent, but side effects develop that can produce a poor quality of life. Many patients develop significant sequelae, such as blindness, loss of voice, vaginal and anal stenosis. In most patients cause of death is opportunistic infections secondary to immune suppression. To date, intravenous immunoglobulin (IVIg) has been reported to have benefited 156 patients with AMBDs. Its most important features include the ability to reduce or eliminate conventional therapy, the enabling of clinical control, the ability to induce and maintain long-term clinical remission, the capacity for usage based on a defined protocol with a described end point and a resulting increase in quality of life. IVIg produces the best clinical outcome when combined with aggressive topical therapy, sublesional injections of triamcinolone and rapid detection, and early treatment of cutaneous and mucosal infection. Successful therapy requires a physician to spend significant time with each patient. This manuscript provides the opinion of the author on the current use of IVIg to treat AMBDs.

Comparison of IgG preparations by a turbidimetric assay of opsonizing capacity

A convenient turbidimetric phagocytosis assay was applied for the functional comparison of various intravenous IgG preparations. Staphylococcus aureus (Oxford) was opsonized by the immunoglobulin samples in the presence of an IgG deficient serum as a source of complement. The opsonized bacteria were subjected to phagocytosis by neutrophil granulocytes isolated from healthy adults. The time course of phagocytosis was monitored by the decrease of light absorbance at 400 nm. Changes in light absorbance during a 15 min period of opsonophagocytosis (delta E(400)) were expressed as a percentage of delta E(400) obtained by a reference IgG preparation. The opsonizing effect of five commercially available i.v. IgG preparations was compared. Three different preparations containing whole, non-modified IgG molecules had a comparable opsonizing effect while a further one prepared by propiolacton modification displayed a reduced activity (52%) of the reference preparation, taken as 100%. A preparation consisting of IgG molecules without an Fc-region proved to be practically ineffective (8.7%).

Immunoglobulin preparations for intravenous administration. A review of their biologic activities and comparison of various preparation methods

Substitution therapy with human immunoglobulin preparations is well established in disorders of primary or secondary deficiencies of humoral immunity. However, modifications of the immunoglobulins are required to achieve tolerance for the preferred intravenous route of administration. Several procedures are employed by different commercial suppliers of immunoglobulins, and from the literature it appears that various important biologic functions, e.g., opsonic activity, complement fixation, and Fc-receptor function, are subject to alterations during the preparation. The best preservation of such activity, when assessed in vitro, is obtained with polyethylene glycol precipitation or DEAE-Sephadex fractionation, whereas enzymatic or chemical treatment can potentially reduce the biologic activity. It is recommended that immunoglobulin preparations be evaluated in vitro for intact biologic function before being given to immunodeficient patients.