Since the beginning of the Covid19 pandemic, researchers around the world have tried to understand which factors could correlate with the severity of the disease: an obvious factor is age. We know that the risk of serious illness and death increases and correlates with the age of patients and this phenomenon is partially explained by the fact that, as we age, our immune system gradually deteriorates. Another risk factor is the presence of auto-antibodies to interferon, which limit the natural immune response against the virus. In this recent work, the researchers studied the cell-mediated response, that is, that arm of the immune system composed of T lymphocytes.
T lymphocytes are real cells that identify and kill viruses through a series of complex mechanisms. The cell-mediated response joins the humoral one, characterized by antibodies which are proteins capable of attaching themselves to specific parts of the virus, blocking or neutralizing it. In viral infections, humoral and cell-mediated responses play a fundamental role in limiting and countering viral replication and the damage that derives from it.
Those who responded best had more T cells
The researchers studied a group of patients who responded differently to Covid19 (with mild, moderate and severe responses) and noted that patients with milder responses had more T lymphocytes in their blood in the early stages of infection. Conversely, patients who contracted severe disease instead produced delayed T lymphocytes.
Furthermore, the researchers observed that patients with milder disease were not only able to produce T lymphocytes in the early stages of infection, but the T lymphocytes produced were also targeting more parts of the virus. T lymphocytes, similar to antibodies, are specialized towards a viral protein, for example CD4 + anti-spike lymphocytes: they are able to detect, attack and kill all viruses that have the Spike protein.
Lymphocytes affecting multiple parts of the virus
The T lymphocytes produced in subjects with mild disease were able to affect more parts of the Sars-CoV2 virus thus generating a more complete response.
T lymphocytes, in addition to playing their ‘killer’ role, are also responsible for the production of various substances involved in the antiviral response such as interferons. As observed in the past, individuals with interferon production deficiency develop more severe disease and have a higher risk of death. This study is in line with previous observations and suggests that subjects at severe Covid19 risk produce T lymphocytes in lower quantities, late and have fewer interferons.
TAKE HOME MESSAGES
1 – humoral response and cell-mediated response are essential for fighting infections
2 – there is a correlation between T lymphocyte production and severity of Covid19
3 – people who produce a lot of T lymphocytes in the early stages of infection develop a milder disease
4 – T lymphocytes are not limited to eliminating viruses but are an integral part of the immune response
References:
https://www.mdpi.com/1422-0067/23/13/7155
https://www.repubblica.it/salute/2022/05/30/news/covid_auto_anticorpi_indicatori_rischio_morte-351418195/