28 Sep 2023
Antibodies in the eyes, nose, mouth and throat most effective at protecting against emerging COVID-19 variants
Mucosal surfaces, the wet linings in the eyes, nose, mouth and throat, play a crucial role as the first in line of defence against upper respiratory infections, such as COVID-19. Understanding how the mucosal immune system responds to COVID-19 infection and vaccination is important for planning effective long-term immunity strategies, especially against new variants of the virus.
In world-first research published in JCI Insight and Immunology & Cell Biology researchers led by the Doherty Institute examined how antibodies in saliva and tears work together to protect against infections and regulate the immune system.
Specifically, the team compared levels of antibodies in blood, saliva and tears from individuals with different types of mixed immunity – infection then vaccination vs. vaccination then infection, and detected differences arising from prior mucosal exposure due to infection.
University of Melbourne’s Dr Kevin John Selva, a Research Officer at the Doherty Institute and first author of the papers, said following vaccination, both groups produced good levels of immunoglobulin G (IgG) antibodies, the main type of antibodies found in the blood, but that immunoglobulin A (IgA) antibodies, the key antibody type found in mucosal secretions, only increased in individuals who had been infected with COVID-19 before vaccination.
“We found that, alone, vaccination does not induce mucosal antibodies. However, receiving vaccines after recovering from a COVID-19 infection boosts mucosal antibodies which also become more effective at binding to receptors on immune cells to clear the virus,” said Dr Selva.
“These results indicate that previous exposure to SARS-CoV-2 through the mucosal route may be necessary to improve localised antibody protection at the mucosal surfaces.”
University of Melbourne’s Associate Professor Amy Chung, Lead of the Discovery Research cross-cutting discipline at the Doherty Institute and co-senior author of the papers, said that the ability to recognise the virus was not consistent among the different types of antibodies.
“Interestingly, our findings show that IgG antibodies in the bloodstream can mostly recognise the original virus, while mucosal IgA antibodies is able to target both the ancestral virus and the newer variants,” said Associate Professor Chung.
For the team, this work demonstrates the value of constantly updating COVID-19 vaccines and supports the global push towards developing vaccines that can induce better local mucosal protection.
Peer Review:
JCI Insight, https://doi.org/10.1172/jci.insight.172470
Immunology & Cell Biology, https://doi.org/10.1111/imcb.12685
Funding: Medical Research Future Fund (MRFF), NHMRC and NMRC Singapore.