Cells of the Immune System

  • Lymphocytes are the central cells of the immune system, responsible for acquired immunity & the immunologic attributes of diversity, specificity, many and self/non-self recognition.
  • Lymphocytes constitute 20% to 40% of the body's WBC and 99% of the cells in the lymph.
  • Resting B & T-lymphocytes are small, motile, nonphagocytic cells, which can't be distinguished morphologically.
  • In Go - phase of the cell cycle, B and T- lymphocytes are not interacted with antigen-referred to as "naive cells", which have generally short life span.
  • Certain cytokines induces the naive cells to enter the cell cycle by progressing from G0 into G1 & subsequently into S, G2 & M.
  • Lymphoblasts proliferate and differentiate into "Effector cells" (or) into "Memory cells".

  • Effector cells: The functions in various ways to estimate the antigen. These cells have short life spans, generally ranging from a few days to few weeks

  • Plasma cells: The antibody-secreting effector cells of the B-cell lineage have a characteristic cytoplasm that contains abundant ER(to support their rate of protein synthesis).

Lymphocyte dev

  • The lymphocytes can be broadly subdivided into three populations - B-cells, T-cells, Null cells-on the basis of function and cell membrane components.

  4. Other Cells are

B-Cells are involved in Humoral Immune response and

T-cells are involved in Cell mediated immune response.

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Null cells

Null cells are lymphocytes with cytotoxic properties. They are neither B-cells not T cell. They are intermediate between T and B cells. They form less than 3%. There are two types of Null cells namely, Natural Killer Cells (NK cells) and Killer Cells . Natural Killer Cells: NK cells are a group of null cells. They form the third population of lymphocytes. The NK cells have 2 or 3 large granules in the cytoplasm. Hence they are also Large Granular Lymphocytes (LGL). They have a kidney shaped nucleus. The NK cells kill the target cells without the aid of antibody or complement. So they are antibody independent. They destroy the cancer cells and cells infected with herpes and mumps virus . They are activated by Interferons and I nterleukins-2. Killer Cells (K cells): Killer cells are antibody dependent. These cells possess Fc receptors for binding with IgG antibodies. Hence they can bind with cells coated with IgG antibodies and can kill them. These cells can combine
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Lymph node

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Lymph nodes are encapsulated bean-shaped structures containing a reticular network placed with lymphocytes, macrophages & dendritic cells. The overall architecture of a lymph node supports an ideal micro environment for lymphocytes to effectively encounter and respond to trapped antigens. The lymph node can be divided into three roughly concentric regions based on morphology: Cortex: The Cortex contains lymphocytes (mostly B-cells), macrophages & follicular dendritic cells arranged in primary follicles. This cortex region some times referred to as "Thymus-independent area. Medulla: It is innermost layer of lymph node P ara-cortex: Beneath the cortex, which is populated largely by T-Lymphocytes and also contains interdigitating dendritic cells thought to have migrated from tissues to the node. These interdigitating dendritic cells express high levels of class n MHC molecules, which are necessary for presenting antigen to T H -cells. These paracort
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Thymus

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The thymus is a flat, bi-lobed organ situated above the heart. Immature T-cells are simply referred as "Thymocyte", these are densely packed outer compartment (or) cortex of the thymus lobule. Some of the thymic epithelial cells in the outer cortex, called "nurse cells", have long membrane extensions that surround as many as so thymocytes, forming large multicellular complexes The average weight of the thymus is 70 grams in infants; its age dependent involution levels an organ with an average weight of only 3 grams in the elderly. Explanations about Thymus: The thymus covered by a fibrous capsule . It is formed of two lobes. Each lobe of the thymus is organized into lobule which is separated from one another by septa called trabeculae. With in each lobule, the cells are arranged into an outer cortex and an inner medulla. The cortex is tightly packed with proliferating immature lymphocytes while the medulla contains more mature cells. As
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