Question

State four differences between adaptive and innate immune system, then list two reasons why memory B cells respond more quickly than naïve B cells to antigen. Do the same for memory vs naïve T cells.

Answer 1

The differences between Innate and adaptive immunity are as follows:

	Innate Immunity	Adaptive/Acquired Immunity
Definition	Innate immunity is the inborn resistance against infections that an individual possesses right from the birth, due to his genetic or constitutional markup.	Acquired immunity is the resistance against infecting foreign substances that an individual acquires or adapts during the course of life.
Origin	Prior exposure to the antigen is not required. It is present before the first exposure to microbial antigen.	Develops during lifetime  following the antigenic exposure
Activity	Always present	Normally silent but triggers often exposure to pathogens
Diversity	Diversity is limited; It is active only against a limited repertoire of antigens.	Adaptive immunity is more varied and involves specialized immune responses.
Specificity	Non-specific; defend against any pathogen upon first exposure	Antigen specific-responds to specific pathogen on 2nd or latter exposure

When a naive B cell encounters an antigen that fits or matches its membrane-bound antibody, it quickly divides in order to become either a memory B cell or an effector B cell, which is also called a plasma cell. When the naive B cell divides and differentiates, both plasma cells and memory B cells are made. The memory B cells produced during the primary immune response are specific to the antigen involved during the first exposure. In a secondary response, the memory B cells specific to the antigen or similar antigens will respond. When memory B cells reencounter their specific antigen, they proliferate and differentiate into plasma cells, which then respond to and clear the antigen. The memory B cells that do not differentiate into plasma cells at this point can reenter the germinal centers to undergo further class switching or somatic hypermutation for further affinity maturation. Differentiation of memory B cells into plasma cells is far faster than differentiation by naïve B cells, which allows memory B cells to produce a more efficient secondary immune response. So, the response of B cells is faster than naive B cells.

Similar observations are made for T cell. Memory T cells are central to orchestrating antigen-specific recall responses in vivo. Compared to naïve T cells, memory T cells respond more quickly to cognate peptide: MHC with a shorter lag time for entering the cell cycle and exerting effector functions. However, it is now well established that this enhanced responsiveness is not the only mechanism whereby memory T cells are better equipped than naïve T cells to rapidly and robustly induce inflammation. In contrast to naïve T cells, memory T cells are composed of distinct subsets with unique trafficking patterns and localizations. Tissue-resident memory T cells persist in previously inflamed tissue and function as first responders to cognate antigen reexposure. In addition, a heterogeneous group of circulating memory T cells augment inflammation by either rapidly migrating to inflamed tissue or responding to cognate antigen within secondary lymphoid organs and producing additional effector T cells. So, the response of T cells is faster than naive T cells.

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