Immunological memory is an important evolutionary trait that improves host survival upon reinfection. Memory is a characteristic recognized within both the innate and adaptive arms of the immune system.

Immunological memory occurs after a primary immune response against the antigen. Immunological memory is thus created by each individual, after a previous initial exposure, to a potentially dangerous agent. After the primary immune response has disappeared, the effector cells of the immune response are eliminated.

A memory cell is an antigen-specific B or T lymphocyte that does not differentiate into effector cells during the primary immune response, but that can immediately become effector cells upon re-exposure to the same pathogen.

Memory B Cells Typhi (Wahid et al., 2011). The BM cells do not actively secrete antibody but can rapidly turn into mainly IgA antibody–secreting plasma cells upon reexposure to antigen (Crotty et al., 2004); the resulting anamnestic SIgA antibody response may then control infection before it causes disease.

Immunologic memory is another important characteristic of adaptive immunity. It means that the immune system can remember the antigens that previously activated it and launch a more intense immune reaction when encountering the same antigen a second time (Figure 2.10).

Memory cells arise from T-cell dependent reactions in the germinal center and are the critical cell type for immune response to re-challenge from an antigen. Although, like plasma cells, memory B cells differentiate from the GC reaction, they do not secrete antibody and can persist independently of antigen [85].

In addition to the spleen and lymph nodes, memory B cells are found in the bone marrow, Peyers’ patches, gingiva, mucosal epithelium of tonsils, the lamina propria of the gastro-intestinal tract, and in the circulation (67, 71–76).

Memory B cells have several unique features including long lifespan, high sensitivity to low doses of antigen, quick and robust proliferation, and rapid differentiation into plasma cells that produce high-affinity antibodies during the secondary response.

The memory B cells produced during the primary immune response are specific to the antigen involved during the first exposure. When memory B cells reencounter their specific antigen, they proliferate and differentiate into plasma cells, which then respond to and clear the antigen.

Memory B cells could not be activated by a soluble viral protein without T cell help. Transfer of memory B cells into immunocompetent animals indicated that presence of helper T cells did not enhance the memory B cell response.

In this type of RAM, data is stored using the six transistor memory cell. Static RAM is mostly used as a cache memory for the processor (CPU). SRAM is relatively faster than other RAM types, such as DRAM. It also consumes less power.

showed that memory B cell numbers remained constant between 8–20 weeks post-immunization, and based on short-term in vivo BrdU labeling experiments estimated the half-life of memory B cells to be 8–10 weeks (11).

During an immune response, B and T cells create memory cells. These are clones of the specific B and T cells that remain in the body, holding information about each threat the body has been exposed to! This gives our immune system memory.

Memory B cells are generated during primary responses to T-dependent vaccines. They do not produce antibodies, i.e., do not protect, unless re-exposure to antigen drives their differentiation into antibody producing plasma cells.

These are short-term memory T cells. Because they have already battled the virus and reproduced many times, they survive only weeks or months after the initial infection. (T cells can only divide a certain number of times before they die.)

These methods were later used to confirm that memory T cells live for six months or less in healthy humans (Westera et al., 2013), whereas naive T cells can live for up to nine years (Vrisekoop et al., 2008). Thus, a long life is not a key characteristic of memory T cells.

The reason is that immunological memory confers a tremendous survival advantage, as it confers the ability to respond more rapidly and more effectively to a second and subsequent challenge by the same pathogen.

While long-term B cell memory is thought to be maintained by long-lived IgG or IgA secreting cells, it has been proposed that it is also maintained by low avidity IgM-secreting cells which can rapidly proliferate and differentiate into high avidity IgG- or IgA-secreting cells upon encounter with recall antigen.

But if you repeatedly feel anxious and stressed or it lasts a long time, your body never gets the signal to return to normal functioning. This can weaken your immune system, leaving you more vulnerable to viral infections and frequent illnesses. Also, your regular vaccines may not work as well if you have anxiety.

Depression increases your risk of a number of diseases and other conditions by, for example, increasing levels of stress hormones such as cortisol or adrenaline. Depression can affect the immune system, making it harder for your body to fight infection.