Lymph Nodes
During its passage along the lymphatic vessels, lymph flows
through a series of bean – shaped or a gans called lymph nodes. The node
functions as a physical and biological filter, as lymph fluids percolates
through its internal lattice of the cells, the macrophages and lymphocytes survey
the fluids for any bacteria, viruses or foreign macromolecules.
The lymph node cortex usually contains several discrete
spherical or void cellular aggregates called lymphoid follicles. These follicles
are mainly composed of memory B lymphocytes, few T cells and a specialized type
of supporting cell called the follicular dendritic cell. Lymphoid follicles are
labile structures that can disappear and reform at different sites overtime and
can enlarge in response to infections or other immune challenges.
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Primary follicles
Contains predominantly mature, resting B cells, since they
have dense nuclei and little cytoplasm, a primary follicle appears as a relatively
dark staining mass on conventional histological preparation
Secondary follicle
Secondary follicles are not present at birth and they form
only after repeated exposure to substances that provoke an immune response. The
presence of secondary follicles clearly denotes an ongoing B cell immuneresponse.
Spleen
Mucosal Associated Lymphoid tissue (MALT)
Large number of individual T and B lymphocytes, macrophages,
ad plasma cells lies just below the mucosal epithelium in many regions of the alimentary,
genitourinary and respiratory tract. MALT is the largest lymphoid organ
containing roughly half of the lymphoid cells in the body. The important function
of these tissues is to secrete antibodies across the mucosal surface as a
defense against external pathogens