The ABC of ABCS: a phylogenetic and functional classification of ABC systems in living organisms.

ATP binding cassette (ABC) systems constitute one of the most abundant superfamilies of proteins. They are involved not only in the transport of a wide variety of substances, but also in many cellular processes and in their regulation. In this paper, we made a comparative analysis of the properties of ABC systems and we provide a phylogenetic and functional classification. This analysis will be helpful to accurately annotate ABC systems discovered during the sequencing of the genome of living organisms and to identify the partners of the ABC ATPases.

Interest of immunomodulation as a mean to improve the preparation of polyclonal and monoclonal antibody reagents.

Immunomodulation by monoclonal antibodies (mAbs) was investigated in mice in order to improve the preparation of antibody reagents. Three different types of representative immunogens were chosen: a human soluble protein (secretory immunoglobulin A, SIgA), a bacterial polysaccharide from E. coli K1 and an envelope protein from the hepatitis B virus. These Ag are all of importance for diagnosis and exhibit different levels of immunogenicity. Antibody-mediated enhancement was observed against restricted and defined regions of each immunogen i.e.: the Fab epitopes of SIgA, the preS1 domain of the HBV envelope and associated cell wall components of the capsular PS. The epitopes which were enhanced appeared to be different from those recognized by the modulating mAb. Negative modulations were also observed. Moreover, new epitopes seemed to be generated. In both cases the level and direction of the modulation were irrespective of isotypy and affinity of the mAbs. Interestingly the positive modulatory effect was found to be correlated with an in vitro assay based on the binding of immune complex to antigen-presenting cells.

Molecular analysis of the modulatory factors of the response to HBsAg in mice as an approach to HBV vaccine enhancement.

Mice were injected with immune complexes containing the recombinant hepatitis B surface antigen (HBsAg) vaccine (S + preS2) bound to different monoclonal antibodies (mAbs), in order to determine whether an enhancement of the response to a human vaccine could be obtained and observed. Enhancement and indifference were observed, as well as a decrease in immunogenicity. No relationship could be established between any effect and affinity or isotype of the bound mAbs. The preS2 region was rendered more immunogenic when an IgG2a mAb was bound to the S region of the HBsAg. The response to the S region was not modulated, whereas immunogenicity of the preS2 colinear region was decreased by antibody shielding. The mAb which was the most efficient as an enhancer of the antibody response also increased binding of the complexed immunogen to antigen presenting cells. The binding of a human mAb to the sole S region, but not to the preS2 region, should be tested as a potentiating agent of the anti-preS2 human immune response.

Immune complexes as immunizing agents to increase the number of monoclonal antibody producing hybrids and to deviate the response to poorly immunogenic epitopes.

The use of immune complexes (IC) in an antibody excess, as immunizing agent, led to a large increase in the mouse polyclonal response to human SIgA. This enhanced response, as compared to SIgA alone, was analysed with mouse polyclonal anti-alpha chain antibodies (Ab). A kinetic study showed an early rise (between days 14 and 21) of the antibody response against the discontinuous epitopes of SIgA while the anti-IgA response increase was delayed. Induction of hybridomas with an IC consisting in SIgA containing an excess of anti-alpha chain Ab, increased 10-fold the number of positive wells. Moreover, two of these MAb were specific for weakly immunogenic epitopes. One recognized only SIgA (anti-C), i.e. the association between the alpha chain and the secretory component (SC), while the other mainly combined to IgA dimers (anti-P). Both these MAb will be useful tools for structural studies and for the dosage of secretory Ab.