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Immune development

B cell activation and the germinal centre response

B cell activation

B cells are activated when their B cell receptor (BCR) binds to either soluble or membrane bound antigen. This activates the BCR to form microclusters and trigger downstream signalling cascades. The microcluster eventually undergoes a contraction phase and forms an immunological synapse, this allows for a stable interaction between B and T cells to provide bidirectional activation signals. 

T-cell development in thymus

T cells are derived from haematopoietic stem cells that are found in the bone marrow. The progenitors of these cells migrate to and colonise the thymus. The developing progenitors within the thymus, also known as thymocytes, undergo a series of maturation steps that can be identified based on the expression of different cell surface markers. The majority of cells in the thymus give rise to αβ T cells, however approximately 5% bear the γδ T cell receptor (TCR).

Neonatal Immunology

Like many other systems in the body, the immune system is not fully functional at birth and therefore we are at an increased risk of infection. At the same time, the act of being born – moving from the sterile environment of the womb to the wider world, exposes us to a whole range of pathogens that we have never encountered and have no protection against. To supplement this period of immune immaturity and reduce the risk of infection, the mother transfers passive protection to the child, mainly in the form of antibody.