Antibody to mycobacterial 65-kD heat shock protein in commercial antisera

Antibodies against C-reactive protein cross-react with 60-kilodalton heat shock proteins

C-reactive protein (CRP) is an acute-phase reactant frequently used in histochemistry as a marker of ongoing inflammation. Furthermore, CRP is a powerful biomarker for the prediction of coronary artery disease risk. Heat-shock protein 60 (Hsp60) and CRP are complement-activating molecules, and the effect of their interactions on the regulation of complement activation was studied. However, during the first experiments, we learned that polyclonal anti-CRP antibodies cross-react with Hsp60. Therefore, the aim of our present study was to analyze the cross-reactivity of anti-CRP antibodies (Ab) with Hsp60 in solid-phase enzyme immune assays, in epitope studies using a series of overlapping synthetic peptides, and in Ouchterlony analyses. We found that three different commercial rabbit polyclonal antibodies and two monoclonal (9C9 and CRP-8) anti-CRP antibodies specifically recognize recombinant human Hsp60 and recombinant Mycobacterium tuberculosis Hsp65, respectively. Hsp60 was found to inhibit the binding of anti-CRP polyclonal Ab to Hsp60. Six epitope regions of Hsp60 were recognized by the anti-CRP antibodies, and one region (amino acids [AA] 218 to 232) was recognized by monoclonal antibodies CRP-8 and 9C9. This epitope region of Hsp60 displays 26.6% amino acid identity to CRP AA region 77 to 90. These data suggest that the B-cell epitopes shared between CRP and Hsp60 give rise to a true mimicry-based cross-reaction and the induction of cross-reactive antibodies. Our study underlines the importance of thorough study design and careful interpretation of results while using polyclonal anti-CRP antibodies for histochemistry, especially at low dilutions. Furthermore, analytical interference with Hsp60 in CRP assays should also be tested.

Chloroplast PNPase exists as a homo-multimer enzyme complex that is distinct from the Escherichia coli degradosome

In Escherichia coli, the exoribonuclease polynucleotide phosphorylase (PNPase), the endoribonuclease RNase E, a DEAD-RNA helicase and the glycolytic enzyme enolase are associated with a high molecular weight complex, the degradosome. This complex has an important role in processing and degradation of RNA. Chloroplasts contain an exoribonuclease homologous to E. coli PNPase. Size exclusion chromatography revealed that chloroplast PNPase elutes as a 580-600 kDa complex, suggesting that it can form an enzyme complex similar to the E. coli degradosome. Biochemical and mass-spectrometric analysis showed, however, that PNPase is the only protein associated with the 580-600 kDa complex. Similarly, a purified recombinant chloroplast PNPase also eluted as a 580-600 kDa complex after gel filtration chromatography. These results suggest that chloroplast PNPase exists as a homo-multimer complex. No other chloroplast proteins were found to associate with chloroplast PNPase during affinity chromatography. Database analysis of proteins homologous to E. coli RNase E revealed that chloroplast and cyanobacterial proteins lack the C-terminal domain of the E. coli protein that is involved in assembly of the degradosome. Together, our results suggest that PNPase does not form a degradosome-like complex in the chloroplast. Thus, RNA processing and degradation in this organelle differ in several respects from those in E. coli.

Anti-lactoferrin antibodies and other types of anti-neutrophil cytoplasmic antibodies (ANCA) in reactive arthritis and ankylosing spondylitis

Fifty-five serum samples from patients with reactive arthritis (ReA), 40 from patients with ankylosing spondylitis (AS) and three from patients with chronic sacroiliac joint arthritis were analysed for the presence of ANCA of IgG class by means of enzyme immunosorbent assay using lactoferrin (Lf), myeloperoxidase (MPO) and antigen extracted from azurophil granules ('alpha-antigen') containing proteinase 3 (PR3) as substrate. IgG-ANCA were found in 31 (56%) patients with ReA. Twenty-three (42%) had anti-Lf antibodies, nine (16%) had anti-MPO and eight (15%) had anti-alpha-antigen antibodies, none of which reacted with PR3. Only six (14%) AS or sacroiliac joint arthritis patients had ANCA (P < 0.001). Three (7%) had anti-Lf, two (5%) anti-MPO and two (5%) anti-alpha-antigen antibodies. Yersinia and Salmonella bacteria were separated by SDS-PAGE and blots were incubated with serum from rabbits immunized with human Lf. The hyperimmune serum recognized a band of 78 kD from both bacteria which was not seen when preimmune serum was used. The reaction to the 78-kD antigen could be completely inhibited when anti-Lf antibodies were absorbed on Lf coupled to cyanogen bromide-activated Sepharose, possibly indicating cross-reacting epitopes in Lf and enterobacterial antigen.

Distribution of lactoferrin and 60/65 kDa heat shock protein in normal and inflamed human intestine and liver

Immunisation against the mycobacterial heat shock protein (hsp-65) has been proposed to lead to production of autoantibodies against human lactoferrin. Such antibodies occur in ulcerative colitis and in primary sclerosing cholangitis. This study analysed the distribution of hsp-65 and lactoferrin in biopsy specimens from patients with inflammatory bowel disease and primary sclerosing cholangitis and studied whether immunisation against mycobacterial hsp-65 resulted in production of antilactoferrin antibodies and vice versa. Polyclonal rabbit antihuman lactoferrin and monoclonal mouse anti-hsp-65 (ML30) were used for immunohistochemistry on biopsy specimens from patients with inflammatory bowel disease and primary sclerosing cholangitis. Rats were immunised against human lactoferrin and mycobacterial hsp-65 respectively. Antibody measurements were done by enzyme immunosorbent assays. It was found that lactoferrin and hsp-60/65 were not codistributed. Lactoferrin was found on vascular endothelium and in nonparenchymal liver cells both in inflamed and uninflamed tissues, but only in the hepatocytes of inflamed liver. ML30 reactivity was not inhibited by antilactoferrin antibodies. Rat anti-hsp-65 serum had no detectable antilactoferrin antibodies. In conclusion, antilactoferrin antibodies probably do not arise by immunisation against mycobacterial hsp-65. Both nonparenchymal cells and hepatocytes probably participate in clearance of lactoferrin. Endothelial exposure of lactoferrin may have pathogenic implications in diseases with antilactoferrin autoantibodies.