Inappropriate expression of blood group antigens on biliary and colonic epithelia in primary sclerosing cholangitis

ABO blood groups and the risk of SARS-CoV-2 infection

There is no doubt that genetic factors of the host play a role in susceptibility to infectious diseases. An association between ABO blood groups and SARS-CoV-2 infection as well as the severity of COVID-19 has been suggested relatively early during the pandemic and gained enormously high public interest. It was postulated that blood group A predisposes to a higher risk of infection as well as to a much higher risk of severe respiratory disease and that people with blood group O are less frequently and less severely affected by the disease. However, as to the severity of COVID-19, a thorough summary of the existing literature does not support these assumptions in general. Accordingly, at this time, there is no reason to suppose that knowledge of a patient's ABO phenotype should directly influence therapeutical decisions in any way. On the other hand, there are many data available supporting an association between the ABO blood groups and the risk of contracting SARS-CoV-2. To explain this association, several interactions between the virus and the host cell membrane have been proposed which will be discussed here.

"Natural" antibodies and histo-blood groups in biological development with respect to histo-blood group A. A perspective review

The "inappropriate" A-specific ovarian glycosphingolipids discovered in unfertilized C57BL/10J female mice reflect growth processes, which suggest the activity of embryonic stem cells undergoing genetic polymorphism. And the responding anti-GalNAc antibody represents the first classical "natural" antibody, which was unmasked as a highly specific autoantibody. This murine anti-A is subspecifically distinct from the human antibody, discovering by a broader reactivity growth-dependent, xenoreactive A-specific structures also in non-reproductive murine tissues, where an equivalent of the human AB gene family as a cis AB-gene encodes A-and B glycotransferases. Expression of antigen is known to need always more than its encoded enzyme, and the special mechanism which in the C57BL/10J murine ovarian glycospingolipids blocks the expression of "B" still remains still unknown. A herewith arising postulation of a growth-predominating common biological activity may be supported by findings in rats. The number of A-genes here significantly exceeds those of B and in the Wistar rat the A-antigen is only expressed in the wild type, while B-expression requires the transfer of human B. Nevertheless in transgenic rats, the appearance of "A" still remains more pronounced. The observations lead to reports on animals, which do not show AB transferase production or a respective antigen expression in their normal tissues, but inconcistently display A activity in malignant tumors. And respective examples are delivered by phenotype independent neo expressions of "inappropriate" A-specific structures in human cancer. Although in comparison with epitope deletions they are rare, the ubiquitous "natural" (IgM and IgG) anti-A and anti-B levels, against self and not self, irrespective of the blood group in any normal human sera, may reflect invisible "inappropriate" A-specific growth. The role of the associated (auto) anti-B might be different, because B-neo expressions obviously not occur in cancer, and anti-gal-antibodies are supposed to originate primarily from environmental, cross-reactive stimulation, and beyond their functions in defense are otherwise engaged in physiology. In general natural antibody specificities undergo significant phylogenetical changes within the species. However, the in nature wide-spread "natural" anti-A agglutinin specificities survived or even predominated the long-term evolution from the brown trout up to man and still respond to the biological power, i.e. the products of a CAZY glycosyltransferase 6 (ABO) gene family. It is so hypothesized that both, the murine and human "natural" anti-A antibodies represent examples of a still to be analyzed polyclonal response to a provocative, species-independent evolutionary epitope, which arises or escapes by some enzymatic predominance from the genetical polymorphism in a consistent developmental process.

Aetiopathogenesis of primary sclerosing cholangitis

The aetiology and pathogenesis of PSC have not yet been clearly defined. The hypothesis that PSC is an immune mediated disease is supported by associations with HLA haplotypes, the presence of autoantibodies, increased levels of total serum immunoglobulins and the association with other autoimmune diseases. PSC does not, however, have many of the characteristics of classical autoimmunity, particularly the usual female preponderance of disease and lack of a good response to immunosuppression. Non-immune mechanisms such as bacterial infection, ischaemia and toxicity are also clearly important in the development of the disease and these factors may trigger peribiliary inflammation and cytokine-induced hepatic fibrosis. PSC may be triggered in genetically susceptible individuals by toxic or infectious agents gaining access to the liver via a diseased and permeable colon.

Ulcerative colitis: an epithelial disease?

There is now considerable evidence that abnormalities of the structure and function of the colonic epithelium are present in patients with ulcerative colitis and that many of these may occur independently of mucosal inflammation. It is proposed that epithelial abnormalities are the central defect that underlie the development of mucosal inflammation and its chronicity. A simple model for pathogenesis is proposed in which inflammation develops only when epithelial barrier function is impaired to an extent which permits the influx of luminal pro-inflammatory molecules to the lamina propria. Several candidate hypotheses regarding the molecular basis for the abnormality are addressed. The mechanism by which the barrier function is critically impaired involves the interaction of the abnormal epithelium with luminal, mucosal and systemic factors. Focusing on the epithelium would potentially lead to a conceptually different management approach and the development of novel therapeutic strategies.