T-cell immunity

Subject – Science and Tech

Context – COVID-19 vaccines produce T-cell immunity that lasts and works against virus variants

Concept –

A T cell is a type of lymphocyte.
T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response.
T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their cell surface.
T cells are born from hematopoietic stem cells, found in the bone marrow.
Developing T cells then migrate to the thymus gland to mature. T cells derive their name from this organ where they develop (or mature).
After migration to the thymus, the precursor cells mature into several distinct types of T cells.
T cell differentiation also continues after they have left the thymus. Groups of specific, differentiated T cell subtypes have a variety of important functions in controlling and shaping the immune response.
One of these functions is immune-mediated cell death.
They recognise foreign particles (antigen) by a surface expressed, highly variable, T cell receptor (TCR).
There are two major types of T cells: the helper T cell and the cytotoxic T cell.
As the names suggest, helper T cells ‘help’ other cells of the immune system, whilst cytotoxic T cells kill virally infected cells and tumours.
The severity of disease can depend on the strength of these T cell responses.

How the immune system works?

The immune system protects us from various infectious diseases, caused by bacteria, viruses, fungi or parasites. To do this, it first determines what type of infectious agent, or pathogen, is causing the infection. Then it mounts an appropriate response. Crucially, at the same time it produces memory cells that can recognise the same pathogen in future. That sets the immune system up to fight potential reinfections.
If the immune system determines that an antiviral response is needed, it launches a combination of two kinds of immunity. One is mediated by antibodies and the other is mediated by T-cells, or cell-mediated. The antibodies bind to viruses and neutralise them, preventing them from infecting cells. Meanwhile, T-cells kill cells that have already been infected by the virus.
While both kinds of immunity are important in fighting viruses, cell-mediated immunity is far more effective at eradicating viruses and more durable. This is important in the continuing fight against COVID-19.