Fler nedslående nyheter som vi hoppas inte stämmer. Igår pratade jag om att tidigare coronainfektioner skulle kunna ge ett visst skydd speciellt hos unga vilket skulle förklara att det är de äldre som är hårdast drabbade. Tyvärr är det kanske inte så enkelt.
När det gäller vacciner och SARS-CoV-2 så ser det osäkert ut. Jag tittade lite på vaccin för denguefeber där man har sett det paradoxala i att vaccinerade blir värre sjuka vid nästa smittillfälle. Sjukdomen verkar få ett okontrollerbart förlopp hos dem. När jag tittade vidare så handlade det som jag trodde om immunförsvar som löper amok och orsakar bl.a. cytokinstorm och i fallet denguefeber massiva blödningar. Denguefeber finns i fyra olika varianter. Det verkar som att fenomenet också uppstår när någon som varit smittad med en variant återsmittas av en annan. Fenomenet tror man ligger i något som man kallar för
Antibody-dependent enhancement (ADE):
Antibody-dependent enhancement (ADE), sometimes less precisely called immune enhancement or disease enhancement, is a phenomenon in which binding of a virus to non-neutralizing antibodies enhances its entry into host cells, and sometimes also its replication.[1] This phenomenon—which leads to both increased infectivity and virulence—has been observed with mosquito-borne flaviviruses such as Dengue virus, Yellow fever virus and Zika virus,[2][3] with HIV, and with coronaviruses.
There are various hypotheses on how ADE happens and there is a likelihood that more than one mechanism exists. In one such pathway, some cells of the immune system lack the usual receptors on their surfaces that the virus uses to gain entry, but they have Fc receptors that bind to one end of antibodies. The virus binds to the antigen-binding site at the other end, and in this way gains entry to and infects the immune cell. Dengue virus can use this mechanism to infect human macrophages, if there was a preceding infection with a different strain of the virus, causing a normally mild viral infection to become life-threatening.[4]
An ongoing question in the COVID-19 pandemic is whether—and if so, to what extent—COVID-19 receives ADE from prior infection with other coronaviruses.[5]
ADE can hamper vaccine development, as a vaccine may cause the production of antibodies which, via ADE, worsen the disease the vaccine is designed to protect against. Vaccine candidates for Dengue virus and feline infectious peritonitis virus (a cat coronavirus) had to be stopped because they elicited ADE
https://en.wikipedia.org/wiki/Antibody-dependent_enhancement
Vad har nu detta att göra med SARS-CoV-2? Jo, man har sett samma fenomen hos coronavirus och man kan anta att även SARS-CoV-2 har sådana egenskaper. Hos katter finns det ett coronavirus där man har försökt ta fram vaccin men möts av bakslag just precis av den orsaken. Katterna har blivit allvarligare sjuka efter vaccinering:
The feline infectious peritonitis virus (FIPV) is an alphacoronavirus that is a very common pathogen in both domestic and wild cats.[7] It is believed that FIPV can cause antibody-dependent enhancement (ADE). Thus, vaccination against FIPV surprisingly increases the disease seriousness.[8] Moreover, it was demonstrated that infection of macrophages by FIPV in vitro can be triggered by non-neutralising monoclonal antibodies targeting the Spike (S)-protein, and this phenomenon can also occur with diluted neutralising antibodies.[9] ADE explains why half of cats develop peritonitis after being passively immunized with antivirus antibodies and being challenged with the same FIPV serotype.[10] In several countries an attenuated virus vaccine is available in a form of nasal drops; however, its application is still considered controversial by many experts, both in terms of safety and efficacy.[11] The mechanism of antibody-dependent enhancement for FIPV is illustrated in the video. [1]
https://en.wikipedia.org/wiki/Antibody-dependent_enhancement#Alphacoronavirus
Så det ser ut som att man kan stöta på samma problematik hos betacoronavirus som SARS-CoV-2.
ADE verkar bero på ett dysfunktionellt immunförsvar som "misständer". I fallet denguefeber kan det vara imperfekta antikroppar från andra varianter som orsakar fenomenet. Vi vet ju att hos coronavirus kan antikropparna avta med tiden men att det kvarstår någon form av immunitet med hjälpa av minnesceller. Kan det tillståndet ställa till med problem om ett nytt virus som SARS-CoV-2 gör entré? Vad är det egentligen som gör att vissa ofta vuxna utvecklar allvarliga tillstånd som cytokinstorm? Kan det ha att göra med tidigare infektioner av coronavirus eller något specifikt sådant? Frågorna är många men måste besvaras innan man går vidare med utveckling av vaccin åtminstone. Här är två studier som belyser problematiken med ADE och SARS-CoV-2:
Is COVID-19 receiving ADE from other coronaviruses?
Abstract
One of the most perplexing questions regarding the current COVID-19 coronavirus epidemic is the discrepancy between the severity of cases observed in the Hubei province of China and those occurring elsewhere in the world. One possible answer is antibody dependent enhancement (ADE) of SARS-CoV-2 due to prior exposure to other coronaviruses. ADE modulates the immune response and can elicit sustained inflammation, lymphopenia, and/or cytokine storm, one or all of which have been documented in severe cases and deaths. ADE also requires prior exposure to similar antigenic epitopes, presumably circulating in local viruses, making it a possible explanation for the observed geographic limitation of severe cases and deaths.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7102551/
Is antibody-dependent enhancement playing a role in COVID-19 pathogenesis?
The pathogenesis of COVID-19 is currently believed to proceed via both directly cytotoxic and immune-mediated mechanisms [1]. An additional mechanism facilitating viral cell entry and subsequent damage may involve the so-called antibody-dependent enhancement (ADE). ADE is a very well-known cascade of events whereby viruses may infect susceptible cells via interaction between virions complexed with antibodies or complement components and, respectively, Fc or complement receptors, leading to the amplification of their replication [2] (fig. 1). This phenomenon is of enormous relevance not only for the understanding of viral pathogenesis, but also for developing antiviral strategies, notably vaccines.
https://smw.ch/article/doi/smw.2020.20249