Calls for Covid-19 studies to focus on mucosal immunity

More Covid-19 studies should be devoted to how immunity to coronavirus emerges in the mucous membranes of the nose and mouth, scientists have said.

Researchers at the University at Buffalo in the US have expressed concern that the mucosal immune system has not been a focus of much of the research on Sars-Cov-2, the virus that causes Covid-19, despite being the immune system’s largest component.

Professor Michael W Russell, emeritus professor at the department of microbiology and immunology at the University at Buffalo, said: “As mucosal immunologists with several decades of experience behind us, we have been perturbed at the lack of attention to this, and we hope to draw attention to this glaring omission.

“After all, the mucosal immune system is by far the largest component of the entire immune system, and it has evolved to protect the mucosal surfaces where the great majority of infections arise.”

Prof Russell noted that research on Covid-19 initially focused on the cases of severe disease “where the immune responses exacerbate the inflammation rather than fight the infection”.

This is when the virus descends into the lower respiratory tract, especially the lungs.

But he said that since the upper respiratory tract, including the nose, tonsils and adenoids – small lumps of tissue at the back of the nose – are the initial point of infection for the virus, the immune responses that are triggered there are of special interest.

He also said that the high rate of asymptomatic transmission of Covid-19 is another reason why mucosal immunity is so important.

Prof Russell said: “Given that many infected people remain asymptomatic, and that a large number of those who develop symptoms suffer only mild to moderate disease, this suggests that something, somewhere, does a fairly good job of controlling the virus.

“Could it be that this is due to early mucosal immune responses that succeed in containing and eliminating the infection before it becomes serious?

“We will not know unless these questions are addressed.”

In a paper published in the journal Frontiers in Immunology, the authors recommend that studies are needed to determine the nature of an antibody known as immunoglobulin A (SIgA), which plays a crucial role in the immune function of mucous membranes.

They said a focus on mucosal immunity might also make it possible to develop a nasal vaccine, that could be easier to store, transport and administer.

Prof Russell said: “The potential advantage of a mucosal vaccine – especially one that is intranasal – is that it should induce immune responses, including SIgA antibodies, in the mucosal tracts, in this case especially the upper respiratory tract, where the coronavirus makes first contact.”