T cells, just like B cells (that produce antibodies), happen to be the central players with regards to immune response to the viral infection.
What do the researchers say?
Researchers state that when SARS-CoV-2 virus (causing Covid-19) goes on to infect epithelial cells like the ones found airways, it imitates inside cells, making use of biochemical machinery of the host cell. The host cell would thus undergo programmed cell death, thereby releasing molecules named “damage-associated molecular patterns (say – oligomers and nucleic acids).
The molecules get recognized by neighbouring epithelial and endothelial cells and macrophages, thereby resulting them in producing pro-inflammatory cytokines, inclusive of chemokines (Box 1). They could be exemplified as –
- Interleukin-6 [IL-6]
- Monocyte chemoattractant protein 1 [MCP-1, better known as CCL2]
- Macrophage inflammatory protein 1α and 1β
- Interferon gamma-induced protein 10 [IP-10, better known as CXCL 10]
Macrophages, monocytes, and T cells are later recruited to infectious site by the chemokines and various other cytokines that promote inflammation further. These recruited T cells do produce interferon-gamma (IFNγ) as an inflammatory response. There is an involvement of numerous kinds of T cells in this response.
CD4+ helper (Th) cells do enable interaction with CD8+ T cells. These cells, in turn, do drive cytotoxic response (that does kill cells that are infected with virus). These CD8+ T cells do recognize the viral peptides that are presented at surfaces of the infected cells, the same infected cells causing apoptosis (form of “programmed cell death”) and averting the further spread of virus.
CD4+ T cells do have a specialized subset called TFH (Follicular Helper T) that make way for B cells through release of cytokines as well as cell-cell interactions. This reaction gives rise to antibodies by B cells.
Neutralized viruses and apoptotic cells (that are killed by CD8+ T cells) do recognize alveolar macrophages. The viral infection gets cured then.
Studies suggest that patients affected with SARS-Cov-2 have gone with 4-7 days of incubation time prior to onset of the symptoms, and 7-10 days prior to progression to serious disease.
Spanish researchers to Add
Spain-based researchers have identified numerous existing strains of SARS-CoV-2 along with future variants that do have potential for escaping immune system’s cytotoxic T cell response in certain portion of population. HLA molecules encode T cell response in the human beings. There are different HLAs for different individuals, such that it’s programmed for recognizing the invading pathogens based on epitopes of pathogens.
The team mentioned above has discovered 1,222 epitopes related to SARS-CoV-2, which had been associated with the prime HLA subtypes. This covers close to 90% of human population, i.e. 9 out of 10 people could launch T cell response to Coronavirus on the basis of 1,222 epitopes.
Further studies suggest that close to 47% of epitopes were mutated in atleast one isolate that exists. In certain cases, the existing isolates did have mutations in several epitope regions, but cumulative mutations affected only 15% of the epitopes for any type of HLA allele. IFNγ
The good news is that in spite of the fact that Omicron variant has the capability of escaping responses, T cell immune responses still resist numerous variants in majority of individuals with previous SARS-CoV-2 infection.