IgA-mediated clearance and tissue deposition of dinitrophenylated human serum albumin at various DNP:HSA ratios

Mechanistic Analysis of the Effect of Deamidation on the Immunogenicity of Anthrax Protective Antigen

The spontaneous modification of proteins, such as deamidation of asparagine residues, can significantly affect the immunogenicity of protein-based vaccines. Using a "genetically deamidated" form of recombinant protective antigen (rPA), we have previously shown that deamidation can decrease the immunogenicity of rPA, the primary component of new-generation anthrax vaccines. In this study, we investigated the biochemical and immunological mechanisms by which deamidation of rPA might decrease the immunogenicity of the protein. We found that loss of the immunogenicity of rPA vaccine was independent of the presence of adjuvant. We assessed the effect of deamidation on the immunodominant neutralizing B-cell epitopes of rPA and found that these epitopes were not significantly affected by deamidation. In order to assess the effect of deamidation on T-cell help for antibody production elicited by rPA vaccine, we examined the ability of the wild-type and genetically deamidated forms of rPA to serve as hapten carriers. We found that when wild-type and genetically deamidated rPA were modified to similar extents with 2,4-dinitrophenyl hapten (DNP) and then used to immunize mice, higher levels of anti-DNP antibodies were elicited by wild-type DNP-rPA than those elicited by the genetically deamidated DNP-rPA, indicating that wild-type rPA elicits more T-cell help than the genetically deamidated form of the protein. These results suggest that a decrease in the ability of deamidated rPA to elicit T-cell help for antibody production is a possible contributor to its lower immunogenicity.

The involvement of Kupffer cells in the clearance of high molecular weight rat IgA aggregates in rats

In the present study the clearance kinetics and tissue distribution of aggregated 125I-labelled monoclonal rat IgA [( 125I] AIgA) of different sizes were studied in rats. Soluble [125I]AIgA disappeared from the circulation in a biphasic manner with an initial rapid distribution half-life (T1) and a second slower half-life (T2). T2 was directly related to the size of the aggregates. High molecular weight [125I]AIgA, containing 10-12 IgA molecules per aggregate [( IgA]10-12), was cleared much faster than low molecular weight aggregates. The main site of clearance was the liver. The larger the size of the AIgA, the more degradation products were found in the circulation. After injection of [IgA]10-12, non-parenchymal cells (NPC) contained three times more radioactivity than parenchymal cells (PC) (NPC:PC ratio 3.06 +/- 0.96). Ratios of 0.82 +/- 0.03 and 0.62 +/- 0.12 were observed when [IgA]5-6 and [IgA]2 were injected respectively, suggesting a greater role for Kupffer cells in the clearance of large-sized IgA aggregates. Kupffer cells were shown to be the main cells for localization of large-sized AIgA established by immunohistochemical staining on liver cryostat sections.