What Is The Function Of The Immune System

Function Of Lymphoreticular System

The lymphoreticular system is responsible for immigration
response to and it consists of lymphoid and reticuloendothelial components. The same lymphoid cell (lymphocytes and plasma cells) are responsible for specific

The phagocytic cells (polymorphonuclear leucocytes and
macrophages) which one is part of the reticuloendothelial system, are you
mainly concerned with scavenger functions, of eliminating microorganisms and
other foreign particles from blood and tissue, thus contributing to
non-specific immunity.


Lymphoid cells example:-

  • Lymphocytes
  • Plasma

Lymphoid organs

A. Central
(primary) lymphoid organs examples

  • Thymus
  • Bursa of Fabricius in birds
  • Bone marrow in mammals

B. Peripheral
(Secondary) lymphoid organs Example

  • Spleen
  •  Lymph nodes
  •  Mucosa-associated lymphoid tissue (MALT)
  • Lymphoid tissues in
    gut, lungs, liver, bone marrow


The specific time immune response to an antigen can be of
two types:

1. The humeral or antibody-mediated immunity(HMI or AMI). It is medicated by antibodies which are produced by plasma
center cells.

2. The cell medicated and immunity CMI. It is medicated by
sensitized lymphocytes. The central lymphoid organs are structure in which
precursor lymphocytes proliferate, develop, and become immunologically

After acquiring immunological capabilities, the
lymphocytes migrate to peripheral lymphoid organs, where an appropriate immune response occurs when exposed to an antigen.

The cell of the Lymphoreticular System

These consist of the structural cell(reticulum cells,
endothelial cells, and fibroblast and immunologically competent cells (
lymphocytes, plasma cells, and macrophages). In the circulating blood, about 70% lymphocyte are T-
lymphocytes, 70 percent B- lymphocyte, and 10 percent Null-cells.

1. T-Lymphocytes

T-lymphocytes can be classified into the different subpopulation
or subsets based on functional capacity and on surface antigenic determinants.

Based on the surface pro antigenic determination

  • The surface antigen on the T cell can be detected by
    monoclonal antibodies.
  • These thymic antigens or makers were previously designated
    by letter T1 to T11.
  • The markers are now designated as CD(clusters of

2. Null Cells

The small proportion of lymphocytes which are neither
t-cells nor B cells are known as null cells. Among the null cell, killer cell k-cell, natural killer
cell Nk-cell, and lymphokine-activated killer (LAK) cells are recognized. K
cells are now classified with NK cells.

A. Killer Cells(K-Cells)

These lymphocyte posses surface receptor for the Fc portion of
IgG. These cells are capable of doing killing target cells
sensitized with IgG antibodies. They do not require a complement for such lysis
or killing. These are responsible for antibody-dependent cell-mediated cytotoxicity(ADCC).

B. Natural Killer Cell (NK-Cells)

Natural killer cell Nk cells are cytolytic for virally
transformed target cells, certain tumor lines, and involved in allograft
rejection. Nk cells are found in the spleen and peripheral blood. The action of NK cells is independent of antibodies in contrast
to K cells which are dependent on the antibody.

Their activity is natural or nonimmune as it does not require sensitization by prior
antigenic contact. They release several cytolytic factors. NK cells’ activity is enhanced by interferon. It is believed that NK cells play an important role in
antiviral and antitumor immunity.

C. Lymphokine activated killer cells (LAK Cell)

These are the NK cells treated with interleukin-2 (lL-2),
which are cytotoxic to tumor cells without affecting normal cells.

3. B-lymphocytes and Plasma Cells

Antigenically stimulated B-lymphocytes to undergo blast
transformation to become plasma cells. Plasma cells can synthesize an antibody of single
specificity of the single immunoglobulin class (IgM or IgG or IgA).
Interaction of T lymphocytes and B lymphocytes in cell-mediated immunity (CMI)
and humoral or antibody-mediated immunity (AMI).

Major Histocompatibility complex(MHC)

Transplants from one individual to another member of the
same species are recognized as foreign and rejected. The antigens responsible for allograft rejection in inbred
mice were identified and lead to the discovery of the major histocompatibility

The MHC in human is known as the human leukocyte antigen
(HLA) complex. The major transplantation antigens of man include
carbohydrate and glycoprotein antigen of the cell membrane(HLA system)

The HLA Complex

  • Histocompatibility antigens mean cell surface antigens
    that evoke an immune response to an incompatible host resulting in allograft
  • These allogeneic are present on the surface of leukocyte in
    man and are called human leukocyte antigen(HLA) and the set of genes coding for
    they are named the HLA complex.
  • The HLA complex of genes is located on the short arm of
    chromosome 6 and is grounded for in three classes
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