Q. What is the news?
A. At least six papers published in reputable journals — Cell, Nature, Science, and Science Immunology — have found that 2050% of people who have not been infected with novel coronavirus (SARSCoV2) harbour memory T cells derived from previous exposures to common cold coronaviruses.
The memory T cells were found to cross-react with SARSCoV2.
Q. Do the presence of memory T-Cell prevent infection from novel coronavirus?
A. According to various studies, Memory T cells may only reduce COVID19 severity.
The immune cells may mount a faster and stronger response upon exposure to the SARS-CoV-2 virus, but not totally prevent infection.
Q. What is T-Cell?
- T Cells also called T lymphocyte, type of leukocyte (white blood cell) that is an essential part of the immune system.
- T cells are one of two primary types of lymphocytes—B cells being the second type—that determine the specificity of the immune response to antigens (foreign substances) in the body.
- T cells originate in the bone marrow and mature in the thymus.
Q. Why are they called memory cells?
- In the thymus, T cells multiply and differentiate into helper, regulatory, or cytotoxic T cells or become memory T cells.
- They are then sent to peripheral tissues or circulate in the blood or lymphatic system.
- Once stimulated by the appropriate antigen, helper T cells secrete chemical messengers called cytokines, which stimulate the differentiation of B cells into plasma cells (antibody-producing cells).
Q. How do they control immunity?
- Regulatory T cells act to control immune reactions, hence their name.
- Cytotoxic T cells, which are activated by various cytokines, bind to and kill infected cells and cancer cells.
- Because the body contains millions of T and B cells, many of which carry unique receptors, it can respond to virtually any antigen.
Q. What are vaccination correlation with T cells?
- There is a possibility that pre-existing T cell memory might influence vaccination outcomes.
- Pre-existing immunity could help elicit better immune responses against novel coronavirus, and these responses can manifest faster.
- Meanwhile, pre-existing immunity could be mistaken as an enhanced efficacy of the vaccine in eliciting immune responses.
- This could be particularly confusing in Phase-1 trials where the vaccine is tested on a small group of healthy participants.
Q. What might be Its drawbacks?
- The pre-existing immunity can reduce the immune responses that the vaccine causes through a mechanism called the “original antigenic sin”.
- It can also lead to antibody-mediated disease enhancement, where antibodies present at sub-neutralising concentrations can actually augment virus infection and cause more severe disease which was seen in the case of chikungunya and dengue.