The Editors of Encyclopaedia Britannica. Once stimulated by binding to a foreign antigen, such as a component of a bacterium or virus , a lymphocyte multiplies into a clone of identical cells. Others, however, mature and migrate via the blood to the peripheral secondary lymphoid organs —mainly, the lymph nodes, spleen, and epithelium-associated lymphoid tissues in the gastrointestinal tract, respiratory tract, and skin see Figure The diversity of lymphocytes is such that even a single antigenic determinant is likely to activate many clones, each of which produces an antigen – binding site with its own characteristic affinity for the determinant. We shall see that each lymphocyte is committed to respond to a specific antigen and that its response during its first encounter with an antigen ensures that a more rapid and effective response occurs on subsequent encounters with the same antigen.

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Others are secreted and bind to the surface of pathogens, marking them for destruction by either phagocytes or the complement system. Nonactivated T and B cells look very similar, even in an electron microscope. It is impossible to distinguish between T cells and B cells in a peripheral blood smear.

Light, lymphlcyte radiation that can be detected by the human eye. Many cell types in the blood come into contact with these endothelial cells, but only lymphocytes adhere and then migrate out of the bloodstream. The path followed by lymphocytes as they continuously circulate between the lymph and blood. This strong adhesion is mediated by members of the ljmphocyte family of cell adhesion molecules discussed in Chapter 19which become activated on the lymphocyte surface.


Both are activated by antigen to proliferate and mature into effector cells. Most large molecules, including virtually all proteins and many polysaccharides, can serve as antigens.

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Only lymphocytes restored the adaptive immune responses of irradiated animals, indicating that lymphocytes are required lympgocyte these responses Figure Figure Primary and secondary antibody responses. This is unique in that many bacterial infections illustrate neutrophil-predominance instead. The crucial experiments were performed in mice and rats that were heavily irradiated to kill most of their white blood cells, including lymphocytes.

Figure A model for the cellular basis of immunological memory. They are the major components of pus and are found around most common inflammations. The two types of responses work together to eliminate invading pathogens. These antibodies are closely modeled after the receptors of the precursor B celland, once released into the blood and lymph, they bind to the target antigen and initiate its neutralization or destruction. An important requirement of all such cell-transfer experiments is that cells are transferred between animals of the same inbred strain.

In some cancers, such as melanoma and colorectal cancerlymphocytes can migrate into and attack the tumor. Mutant mice, however, that lack the gene encoding C5 but are otherwise genetically identical to the normal mice can make a strong immune response to this blood protein when immunized with it. A simplified drawing of a human lymph lympjocyte.


Lymphocytes Continuously Circulate Through Peripheral Lymphoid Organs Pathogens generally enter the body through an epithelial surface, usually through the skin, gut, or respiratory tract.

Lymphocyte – Wikipedia

Support Center Support Center. Once stimulated by the appropriate antigen, helper T cells secrete chemical messengers called cytokineswhich stimulate the differentiation of B cells into plasma cells, thereby promoting antibody production. Pathologic Basis of Disease lmphocyte ed. Costimulatory signals provided by another specialized cell in a peripheral lymphoid organ are also required. T cell and B cell.

If they encounter their antigen, however, they remain in the node, proliferate, and differentiate into either effector cells or memory cells. Once activated, some of the T cells then migrate to the site of infection, where they help other phagocytic cells, mainly macrophages, destroy the microbes Figure Please try again later.

Hematopoietic stem cell Lymphoblast Prolymphocyte. T cells thymus cells and B cells bone marrow – or bursa -derived cells [a] are the major cellular components of the adaptive immune response.

The binding of antigen to these receptors, however, is usually not sufficient to stimulate a lymphocyte to lymphoctye and differentiate into an effector cell that can help eliminate the pathogen. Effector B cells secrete antibodies. Figure A simplified drawing of a human lymph node.

Some cells of the innate immune system directly present microbial antigens to T cells to initiate an adaptive immune response.