What does a negative Covid-19 antibody test mean?
My results
So as some of you may already know – my recent blood test indicated that I was negative for IgM and IgG antibodies to SARS-CoV-2
What does this mean?
If we take a closer look at the table from my last blog post (I was and remain asymptomatic) – here are the three options available:
Unlikely you have had the infection in the past and you are not immune to getting the infection in the future.
Does not rule out the fact that you have been very recently infected and not produced antibodies.
Possible independent T cell response.
The fact that I have been breathing in Covid-19 infested air in A&E with sloppy social distancing for the last six to seven months means that I am more than certain that I have encountered the virus. I also don’t believe I have been recently infected, but we’ll have to wait and see if I become ill in the coming future.
These things mean that option 1 and 2 are out the window. So, we are left with ‘T cell response’.
T cell response
The immune system is immensely complex. But simply put, we have two major types of immunity- ‘innate’ and ‘adaptive’. The innate immune system is composed of white cells that aren’t pathogen specific and react to foreign material first and quickly. The innate immune system is our first line of defence, it is also the dominant immune system response found in plants, insects and simple multicellular organisms. The innate immune system has no ’memory’ as such.
The adaptive immune system is slower to act and is composed of specialised adaptive white cells which become pathogen specific. B cells and T cells make up the adaptive immune system. Acquired immunity creates immunological memory. It is this immune system which makes the concept of vaccination possible.
As well as describing B cells and antibodies, I have also briefly outlined the different type of T cells and what they do in my previous blog and I recommend reading that to refresh your memory.
The hopeful study
A newly published study titled ‘Robust T cell immunity in convalescent individuals with asymptomatic or mild COVID-19’ by Karolinska University Hospital has been making the rounds in the media recently.
And here’s why – this is their one sentence summary –
‘SARS-CoV-2 induces robust memory T cell responses in antibody-seronegative and antibody-seropositive individuals with asymptomatic or mild COVID-19.’
In other words, they found memory T cell activation in those who were antibody negative and positive for the virus.
The experimenters mapped out SARS-CoV-2-specific T cell responses in 203 people which included unexposed individuals as well as exposed family members and individuals with acute or recovering COVID-19. They found different SARS-CoV-2-specific T cells being activated with various clinical markers of disease severity.
The paper optimistically concludes by saying ‘Our collective dataset shows that SARS-CoV-2 elicits robust memory T cell responses akin to those observed in the context of successful vaccines, suggesting that natural exposure or infection may prevent recurrent episodes of severe COVID-19 also in seronegative individuals.’’
Interestingly the paper also analysed those who were in my boat with negative antibodies or ‘seronegative individuals’ and found SARS-CoV-2-specific CD4+ and CD8+ T cell responses in these individuals too.
So, all in all, yes I probably do have circulating SARS-CoV-2-specific CD4+ and CD8+ T cells.
But does that mean I am immune?
More questions.
Studies with SARS-CoV-1 show that immunity with virus-specific memory T cells to last for many years after its infection, even with antibody responses waning. Studies on mice exposed to SARS-CoV-1 vaccine with no antibodies seem to be protective.
More work is needed to find out whether this is also true with SARS-CoV-2.
Promisingly so, if this is the case, we have to ask ourselves:
- Are more people naturally immune to Covid-19 than first thought?
- Should we also be checking T cell responses in people?
- Should lockdown be stopped sooner than later if both questions above are true?
- Is an international vaccine necessary?
I’ll let you decide.
References
https://www.biorxiv.org/content/10.1101/2020.06.29.174888v1.full.pdf
https://www.ecdc.europa.eu/en/covid-19/latest-evidence/immune-responses
https://www.independent.co.uk/news/world/europe/coronavirus-antibody-test-immunity-levels-study-sweden-a9595491.html
