The Contribution of Liver Sinusoidal Endothelial Cells to Clearance of Therapeutic Antibody

Many chronic inflammatory diseases are treated by administration of “biological” therapies in terms of fully human and humanized monoclonal antibodies or Fc fusion proteins. These tools have widespread efficacy and are favored because they generally exhibit high specificity for target with a low toxicity. However, the design of clinically applicable humanized antibodies is complicated by the need to circumvent normal antibody clearance mechanisms to maintain therapeutic dosing, whilst avoiding development of off target antibody dependent cellular toxicity. Classically, professional phagocytic immune cells are responsible for scavenging and clearance of antibody via interactions with the Fc portion. Immune cells such as macrophages, monocytes, and neutrophils express Fc receptor subsets, such as the FcγR that can then clear immune complexes. Another, the neonatal Fc receptor (FcRn) is key to clearance of IgG in vivo and serum half-life of antibody is explicitly linked to function of this receptor. The liver is a site of significant expression of FcRn and indeed several hepatic cell populations including Kupffer cells and liver sinusoidal endothelial cells (LSEC), play key roles in antibody clearance. This combined with the fact that the liver is a highly perfused organ with a relatively permissive microcirculation means that hepatic binding of antibody has a significant effect on pharmacokinetics of clearance. Liver disease can alter systemic distribution or pharmacokinetics of antibody-based therapies and impact on clinical effectiveness, however, few studies document the changes in key membrane receptors involved in antibody clearance across the spectrum of liver disease. Similarly, the individual contribution of LSEC scavenger receptors to antibody clearance in a healthy or chronically diseased organ is not well characterized. This is an important omission since pharmacokinetic studies of antibody distribution are often based on studies in healthy individuals and thus may not reflect the picture in an aging or chronically diseased population. Therefore, in this review we consider the expression and function of key antibody-binding receptors on LSEC, and the features of therapeutic antibodies which may accentuate clearance by the liver. We then discuss the implications of this for the design and utility of monoclonal antibody-based therapies

Description of Staphylococcus Serine Protease (ssp) Operon in Staphylococcus aureus and Nonpolar Inactivation of sspA-Encoded Serine Protease

Signature tagged mutagenesis has recently revealed that the Ssp serine protease (V8 protease) contributes to in vivo growth and survival of Staphylococcus aureus in different infection models, and our previous work indicated that Ssp could play a role in controlling microbial adhesion. In this study, we describe an operon structure within the ssp locus of S. aureus RN6390. The ssp gene encoding V8 protease is designated as sspA, and is followed by sspB, which encodes a 40.6-kDa cysteine protease, and sspC, which encodes a 12.9-kDa protein of unknown function. S. aureus SP6391 is an isogenic derivative of RN6390, in which specific loss of SspA function was achieved through a nonpolar allelic replacement mutation. In addition to losing SspA, the culture supernatant of SP6391 showed a loss of 22- to 23-kDa proteins and the appearance of a 40-kDa protein corresponding to SspB. Although the 40-kDa SspB protein could degrade denatured collagen, our data establish that this is a precursor form which is normally processed by SspA to form a mature cysteine protease. Culture supernatant of SP6391 also showed a new 42-kDa glucosaminidase and enhanced glucosaminidase activity in the 29 to 32 kDa range. Although nonpolar inactivation of sspA exerted a pleiotropic effect, S. aureus SP6391 exhibited enhanced virulence in a tissue abscess infection model relative to RN6390. Therefore, we conclude that SspA is required for maturation of SspB and plays a role in controlling autolytic activity but does not by itself exert a significant contribution to the development of tissue abscess infections