Page 440 - Atlas of Histology with Functional Correlations

(interleukins) that start the inflammatory response.

The adaptive immune response targets specific invading foreign organisms

and provides specific, or adaptive, defenses. This response is slower than the
innate immune response, but it produces and retains numerous memory cells that
can respond to the second encounter with the particular antigen that is faster,
stronger, and longer lasting. Production of long-lived memory cells is the main

feature of adaptive immunity. Adoptive immunity also involves two types of
specific responses. These are the humoral immune response and the cell-
mediated immune response. These responses produce antibodies that bind to
the antigens or stimulate cells that destroy foreign matter. Both the B cells and T

cells respond to antigens by different means. Humoral immunity is an
antibody-mediated immunity because the antibodies are secreted to neutralize
pathogens outside the cells. Exposure of B cells to an antigen induces
proliferation and transformation of some B cells into plasma cells. These, in

turn, secrete specific antibodies into blood and lymph that bind to, inactivate,
and destroy the foreign substance or antigens. The activation and proliferation of
B cells against antigens require the cooperation of helper T cells that respond to
the same antigen and the production of cytokines. The presence of the B cells,

plasma cells, and production of antibodies in the blood and lymph is the basis of
the humoral immune response.

Cell-mediated immunity involves the activation of phagocytes, antigen-
specific cytotoxic T cells, and the release of various cytokines in response to
antigens. The T cells proliferate and secrete cytokines to stimulate or activate

other T cells, B cells, and other cytotoxic T cells. T-cell receptors are bound to
the T cells, and the cells themselves bind with antigens. On activation and
binding to target cells, cytotoxic T cells destroy foreign cells by inducing

apoptosis, or programmed cell death, by releasing lytic granules containing
perforin. Perforin creates pores in the plasma membrane and kills the cells. T
cells may also attack indirectly by activating B cells and increasing their
antibody production or stimulating the macrophages. T cells provide specific
immune protection without secreting antibodies; instead, they have surface

receptors for antigens.

Supplemental micrographic images are available at
www.thePoint.com/Eroschenko13e under Lymphoid System.

FIGURE 11.4 | Lymph Node (Panoramic View)

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