T-cell Immunity and cross reactive memory

Subject: Science and tech

Context:

Scientists have found that 20-50% people who have not been infected with novel coronavirus (SARS-CoV-2) still harbour memory T cells derived from previous exposures to common cold coronaviruses. The memory T cells were found to cross-react with SARS-CoV-2

Concept:

• Pre-existing T cell immunity to SARS-CoV-2 could be relevant because it could influence COVID-19 disease severity.
• It is plausible that people with a high level of pre-existing memory CD4+ T cells that recognise novel coronavirus could mount a faster and stronger immune response upon exposure to the virus and thereby limit disease severity
• T cells originate in the bone marrow and mature in the thymus. 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).
• 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.