The immune response of the body to COVID 19 infection is very complex and involves both cell mediated and antibody response. The antibodies are produced by the B lymphocytes and the T lymphocytes are responsible for the cell mediated immunity. The T helper cells or the CD 4 cells help the B cells in the production of the antibodies and the T suppresser cells or the CD 8 cells kill the cells that are infected by the virus. The T cells produce chemicals called cytokines and the cytokines help in the elimination and control of viral illnesses. One of the major cytokines that we know is gamma interferon.
The COVID 19 infection causes lymphopenia which means that it depresses the lymphocytes. In fact, lymphopenia is a very important prognostic feature for the outcome of COVID 19 illness. Both CD 4 and CD 8 cells are affected. The response of these T cells is severely impaired and depressed. The levels of CD 4 and CD 8 cells help in strategizing proper treatment case to case in patients.
When a person is infected with SARS-CoV-2, it infects the epithelial cells. After the replication the cell undergoes a lysis and releases what are known as the damage associated molecular patterns. These molecules are recognized by the macrophages and they produce cytokines that help in the control of the infection. These cytokines are -Interleukin-6 [IL-6] and gamma interferon. Macrophages and T cells are attracted to the site of infection by these chemicals and this results in an inflammatory response by the body.
The CD 4 cells or the T helper (Th) cells along with CD8+ T cells cause a cytotoxic response that results in killing the cells infected with the virus. The CD8+ T cells are capable of recognizing the cells infected by the virus and they cause the death of the cells along with the virus inside thus preventing the spread of the virus to the rest of the body. The CD 4 cell on the other hand help the B cells to produce antibodies against the virus.
In SARS-CoV-2 there is a depletion of CD4+ T cells, CD8+ T cells. This can lead to an impaired or inappropriate immune response to the infection. People who have a high CD 4 response has been linked to recovery.
Not only are the CD4 and CD 8 responsible for the recovery or the response of the individual to the disease, these cells are also important for long term protection and the memory against this Virus