Dextrans antigenicity

Some antigens, such as type 3 pneumococcal polysaccharide, EPS and other polymeric substances such as dextrans (poly-D-glucose) and levan (poly-D-fructose) can induce antibody synthesis without the assistance of TH cells. These are known as T-independent (Ti) antigens. Only one class of immunoglobulin (IgM) is synthesized and there is a weak memory response. 

Zozaya40 reported that nitrogen-free L. mesenteroides dextran was not antigenic, but could be rendered antigenic by adsorption upon a... 

Dextran resulting from the action of another strain of L. mesenteroides (designated for convenience, strain B) was more soluble than strain A dextran and exhibited somewhat different immunological reactions. This strain B dextran reacted only slightly with pneumococcus Type XII antisera and had a narrower zone of antigenic reactivity than the strain A dextran. In addition, the strain A organisms exhibited a greater capacity to absorb antibodies reactive with the B dextran than did the B bacteria to absorb antibodies reactive with the A dextran. 

Manabe, Y., Tsubota, T., Haruta, Y., Okazaki, M., Haisa, S., Nakamura, K., and Kimura, I. (1983) Production of monoclonal antibody-bleomycin conjugate utilizing dextran T40 and the antigen-targeting cytotoxicity of the conjugate. Biochem. Biophys. Res. Comm. 115, 1009. 

Some separation techniques rely on the physical removal of one of the fractions charcoal will strongly adsorb the free fraction allowing its ready removal by centrifugation the addition of dextran reduces the tendency of charcoal to strip bound antigen from the complex alternatively, the bound fraction may be precipitated by the addition of suitable concentrations of various protein precipitants such as alcohol, ammonium sulphate and polyethylene glycol (PEG). 

Avseenko et al. (2001) immobilized antigens onto aluminum-coated Mylar films by electrospray (ES) deposition. Various surface modifications of the metallized films were studied to determine their abilities to enhance sensitivity. The plastic surfaces were firsf cleaned by plasma discharge treatment, followed by coating with proteins (BSA and casein) or polymers such as poly (methyl methacrylate) or oxidized dextran, or they were exposed to dichlorodimethyl silane to create hydrophobic surfaces. Protein antigen was prepared in 10-fold excess sucrose and sprayed onto the surfaces to form arrays with spot diameters between 7 and 15 pm containing 1 to 4 pg protein. 

Antigens and their corresponding antibodies precipitate by cross-linking to form an insoluble network. Polysaccharides have multiple, repetitive immunodeterminants and virtually none have demonstrable tertiary structure in solution (except, perhaps, under viscous stress). The number of these immunodeterminant groupings on each macromolecule is large. In the case of dextran, for instance, there are several thousand of them (if the dextran has a molecular weight of several million), even if the determinant involves the hep-tasaccharide. There is, thus, ample opportunity to form a precipitating, crosslinked complex with divalent (or polyvalent) antibody molecules. 

In contrast to the EPOS system, a modification of the highly sensitive two-step immunohistochemical EnVision system allows the detection of a broad spectrum of antigens in frozen sections in less than 13 min (Kammerer et al., 2001). In this study 38 out of 45 antibodies tested showed specific staining. In fact, the modified EnVision procedure allows the use of any suitable primary antibody, preferably monoclonal antibodies. Like the EPOS system, EnVision employs a dextran polymer coupled to horseradish peroxidase molecules for detection. No attempt was made to block endogenous peroxidase, nor was any antigen retrieval pretreatment used. Because of the very short incubation durations, a humid chamber is not required to avoid evaporation of immunoreagents. 

The enhanced peroxidase one-step (EPOS) method is considered superior to standard ABC technique in that the former is more sensitive than the latter. It is known that the Ki-67 antibody can only be used on fresh or frozen tissues, whereas the monoclonal antibody MIB-1, developed against a part of the Ki-67 antigen molecule, can be used on sections of formalin-fixed and paraffin-embedded tissues using antigen retrieval. Recently, EPOS Ki-67 antibodies were developed which consist of antibody molecules and horseradish peroxidase bound covalently to dextran (Bisgaad et al., 1993). This method has been applied for localizing PCNA and Ki-67 antigens (Tsutsumi et al., 1995). 

Dextran is a physiologically harmless biopolymer because of its biocompatible, biodegradable, non-immunogenic and non-antigenic properties [54, 55]. It can be depolymerised by different a-l-glycosidases (dextranases) occurring in liver, spleen, kidney and lower part of the gastrointestinal tract. 

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