Antiphospholipid antibody production during Mediterranean spotted fever

Identification of cross-reactive epitopes on the conserved 47-kilodalton antigen of Orientia tsutsugamushi and human serine protease

Orientia tsutsugamushi is the causative agent of scrub typhus. One of the protein antigens of this species, the conserved 47-kDa protein (HtrA), has been shown to induce an antibody response in patients and can provide protective immunity against live challenge by Orientia in mice. Pepscan experiments identified many peptide epitope clusters in different parts of this protein. The majority of the most reactive epitopes are located at the C terminus of the protein (from amino acid 333 to amino acid 430). Protein sequence analysis revealed that the 47-kDa protein contains a trypsin domain and has sequence homology to human serine protease HtrA1 (hHtrA1). As the 47-kDa protein is a potential vaccine candidate and its ability to induce autoimmunity is a concern, the reactivity of scrub typhus patient sera with purified recombinant 47-kDa and hHtrA1 proteins was tested. A significant percentage (>20%) of scrub typhus patient sera reacted strongly with recombinant hHTRA1 and two of the antigenic polypeptide epitopes in hHtrA1. These findings suggest that the safety of the full-length 47-kDa antigen as a vaccine candidate is a significant issue due to its cross-reactivity with a human protein, which may also contribute to autoimmune responses or enhanced pathology in some scrub typhus patients.

An epitope shared by cellular cytokeratin and Orientia tsutsugamushi

Many microbial pathogens have epitopes shared with host cell components and these epitopes may induce transient or longer-term tissue-damaging autoantibody responses. We observed that several mouse monoclonal antibodies (MAbs) raised against Orientia tsutsugamushi were also reactive with host cells. One such antibody, MAb Rb105, cross-reacted with the cytoskeleton, as shown by immunofluorescent staining. Biochemical studies identified the cross-reacting component as a cytokeratin protein. These results identify an epitope shared by O. tsutsugamushi and the cytokeratins of host cells. In addition, antibodies cross-reactive with the cytoskeleton were detected in the sera of scrub typhus patients, suggesting that an epitope similar to that detected by MAb Rb105 may be recognized by human antibodies.

Antiphospholipid antibodies: discovery, definitions, detection and disease

Antiphospholipid antibodies (aPL) are immunoglobulins of IgG, IgM and IgA isotypes that target phospholipid (PL) and/or PL-binding plasma proteins. Detection of aPL in the laboratory is done currently by both immunoassays and functional coagulation tests. Convention defines aPL specificity in immunoassays according to the particular PL substrate present, for example aPS represents antiphosphatidylserine antibodies. This may be technically incorrect inasmuch as a particular PL may be responsible for binding and highly concentrating a specific plasma protein, the latter then becomes the target for the aPL. The binding of beta(2)GP-I (apolipoprotein H) to the negatively charged PL, cardiolipin (CL) provides a good example of this circumstance. In contrast, aPL which specifically prolong coagulation times in in vitro are called lupus anticoagulants (LA). The precise PL target(s) of the aPL responsible for LA activities are unknown and often debated. The persistent finding of aPL in patients in association with abnormal blood clotting and a myriad of neurological, obstetrical and rheumatic disorders often compounded by autoimmune diseases has led to an established clinical diagnosis termed antiphospholipid syndrome (APS). The common denominator for these APS patients is the presence of circulating aPL on two or more occasions and the observation of events attributable to abnormal or accelerated blood clotting somewhere in vivo. The purpose of this review is to collect, collate, and consolidate information concerning aPL.

Anti-phosphatidylethanolamine (aPE) antibodies: a survey

Reports of anti-phosphatidylethanolamine antibodies (aPE) with similar or identical pathogenic associations as those described for anticardiolipin (aCL) and anti-phosphatidylserine (aPS) are found in the literature. In some instances, aPE is the sole antiphospholipid antibody (aPL) observed. Lupus anticoagulant antibodies (LA) appear to represent a subset of aPE as hexagonal phase PE can specifically inhibit the LA ability to prolong clotting times. As documented for aPL to the negatively charged phospholipids (PL), plasma proteins have been implicated for a positive aPE signal in the ELISA. Other aPE appear independent of known PE-binding plasma proteins. Among the described PE-binding proteins are high and low molecular weight kininogens (HMWK and LMWK) and the HMWK-binding proteins, factor XI and prekallikrein. Recently prothrombin has been added to this list. The reports of aPE published since 1986 are reviewed and discussed in this presentation.

Circulating lupus anticoagulant and probable systemic lupus erythematosus in a cat

An adult domestic short hair cat was presented in a critical condition with icterus. Various investigations demonstrated the presence of haemolytic anaemia and hepatic abnormalities, as well as significant coagulation defects. Systemic lupus erythematosus (SLE) was suggested as a possible cause.