Question

Covid 19 is caused by a novel coronavirus strain, not seen in the human population until now. Describe the clonal selection theory. How might clonal selection be impacting the spread of this disease and human resistance to infection?  

Answer 1

Explanation- Clonal selection theory is accepted as an underlying paradigm of modern immunology in developing adaptive immunity against any specific antigen that may also be in case of novel corona virus strain.

When human body encounters a novel corona virus, it is assumed that it will attach to the surface of any Lymphocyte (B and T cells) carrying reactive sites (BCR and TCR) that correspond to one of virus's antigenic determinant. According to the the clonal selection theory, an individual B or T cell express as many copies of a membrane receptor that is specific for a single or distinct antigen of this virus. This unique receptor specificity is determined in the lymphocytes before it is exposed to the virus or its antigens. Binding of antigenic determinants to the specific receptor activates the cells, causing it to proliferate into a clone of daughter cells that have the same receptor specificity or even increased specificity as compared to the parent cells. Random mutation occur during cell division gradually increases the binding affinity for daughter B cell receptor as explained in clonal selection theory.

B cells now differentiate to form two cells- plasma cells and memory cells. Plasma cells are now capable of active liberation of stable antibodies targeting this novel corona viruses whereas memory cells retained for second subsequent exposure of this virus. Secondary immune responses from Memory cells  are so effective that repeted infection of this virus can be stopped before symptoms even develop. Also following the initial infection, random mutation during clonal selection could produce memory B cells that can more easily stop this viral infection than can the original B cell.

Thus, Human gradually develop resistance to infection against this novel corona virus in similar way as in case of vaccines.