Memory B and T cells

This primary response takes some 10 days and is accompanied by the generation of memory B- and T-cells for secondary immune responses. It should be noted that immunosuppression is more effective for primary responses than for secondary responses. 

Active immunity occurs when the organism is exposed to a toxin or infectious agent (bacterium, virus, or parasite) so that the immune system is stimulated. Most of your parents, grandparents, and instructors contracted measles, mumps and chicken pox when they were children and so are now naturally immune to such agents because their antigenic memory (B and T cells) is primed for a full scale IgG response. 

In an immune response, antibodies are produced and secreted by the B-lymphocytes in conjunction with the T, cells. In the majority of hapten-carrier systems, the B cells end up producing antibodies that are specific for both the hapten and the carrier. In these cases, the T lymphocytes will have specific-binding domains on the carrier, but will not recognize the hapten alone. In a kind of synergism, the B- and T-cells cooperate to induce a hapten-specific antibody response. After such an immune response has taken place, if the host is subsequently challenged with only the hapten, usually it will respond by producing hapten-specific antibodies from memory cells formed after the initial immunization. For a review of immunobiology (see Janeway, 2004). 

Immunological memory, i.e., B cells and T cells that are poised for rapid antibody formation and antigen destruction, provides the molecular basis for the successful use of vaccines. In vaccination, the stimulation of B- and T-cell clones leads to formation of antibodies to the foreign proteins. Differentiation of some of the B cells that recognize the antigen into memory cells provides the mechanisms for resisting subsequent infections. 

Stimulates B and T cell function Behaves as a potent chemoattractant for B lymphocytes induces a weak chemotactic response in T cells and macrophages Provides antimicrobial activity behaves as chemoattractant for immature dendritic cells and memory cells... 

B and T cells, two types of lymphocytes, comprise a special class of mature cell. Upon activation, B and T cells can expand clonally to give rise to both effector and memory cells. Unstimulated memory lymphocytes have very long half-lives, on the order of years to decades. These memory cells can be reactivated at a later time, upon recurrence of an infection, and expand clonaUy, repeatedly. Although memory B and T lymphocytes are unipotent (i.e., they cannot differentiate into a different cell type) their maintenance requires self-renewal capability, an essential property of stem cells. Thus, memory B and T lymphocytes have been called honorary stem cells (Jones and Armstrong 2008). 

The ideal of any vaccine is to provide life-long protection to the individual against disease. Immunological memory (Chapter 14) depends upon the survival of cloned populations of small B and T lymphocytes (memory cells). These small lymphocytes have a lifespan in the body of ca. 15-20 years. Thus, if the immune system is not boosted, either by natural exposure to the organism or by re-immunization, then immunity gained in childhood will be attenuated or lost completely by the age of 30. Those vaccines which provide only poor protection against disease have proportionately reduced time-spans of effectiveness. Yellow fever vaccination, which is highly effective, must therefore be repeated at 10-year intervals, whilst typhoid vaccines are only effective for 1-3 years. Whether or not immunization in childhood is boosted at adolescence or in adult life depends on the relative risks associated with the infection as a function of age. 

As described above, peptide epitopes bound to MHC class I or II molecules are able to stimulate CD8+ and CD4+ T cells, respectively. Both CD4+ T-helper cells and CD8+ CTLs are critical to protective immunity and to vaccine efficacy. CD4+ T-helper cells play an important role in the development of memory B-cell (antibody) and memory CTL (cytotoxic T-cell) responses. CD4+ T-helper cells are also active against pathogens on their own. Therefore, CD4+ T-helper cells have been called the conductors of the immune system orchestra (14). CD8+ CTLs are able to directly kill infected target cells and thus are critical in the containment of... 

Kivisakk P, Mahad DJ, Callahan MK, Trebst C, Tucky B, Wei T, Wu L, Baekkevold ES, Lassmann H, Staugaitis SM, Campbell JJ, Ransohoff RM (2003) Human cerebrospinal fluid central memory Cd4-i- T cells Evidence for trafficking through choroid plexus and meninges via P-selectin. Proc Natl Acad Sci USA 100 8389-8394. 

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