The complement system is a biochemical

The complement system is a biochemical cascade of the immune system that helps, or “complements”, the ability of antibodies to clear pathogens or mark them for destruction by other cells. The cascade is composed of many plasma proteins, synthesised in the liver, primarily by hepatocytes. DELL XPS L501X CPU FAN The proteins work together to:

• trigger the recruitment of inflammatory cells.

"tag" pathogens for destruction by other cells by opsonizing, or coating, the surface of the pathogen. DELL XPS L502X CPU FAN forming holes in the plasma membrane of the pathogen, resulting in cytolysis of the pathogen cell, causing the death of the pathogen.rid the body of neutralised antigen-antibody complexes. Elements of the complement cascade can be found in many nonmammalian species including plants, birds, fish and some species of invertebrates. DELL XPS M1210 CPU FAN All white blood cells (WBC) are known as leukocytes. Leukocytes are different from other cells of the body in that they are not tightly associated with a particular organ or tissue; thus, they function similar to independent, single-celled organisms. Leukocytes are able to move freely and interact with and capture cellular debris, foreign particles, or invading microorganisms. DELL XPS M1330 CPU FAN Unlike many other cells in the body, most innate immune leukocytes cannot divide or reproduce on their own, but are the products of multipotent hematopoietic stem cells present in the bone marrow.^[2] The innate leukocytes include: Natural killer cells, mast cells, eosinophils, basophils; and the phagocytic cells includingmacrophages, neutrophils and dendritic cells, DELL XPS M140 CPU FAN

and function within the immune system by identifying and eliminating pathogens that might cause infection.

Mast cells are a type of innate immune cell that reside in connective tissue and in the mucous membranes. DELL XPS M1530 CPU FAN They are intimately associated with defense against pathogens and wound healing, but are also often associated with allergy andanaphylaxis.^[5] When activated, mast cells rapidly release characteristic granules, rich in histamine and heparin, along with various hormonal mediators, and chemokines, or chemotactic cytokines into the environment. DELL XPS M170 CPU FAN

Histamine dilates blood vessels, causing the characteristic signs of inflammation, and recruits neutrophils and macrophages.

The word 'phagocyte' literally means 'eating cell'. These are immune cells that engulf, i.e. phagocytose, pathogens or particles. DELL XPS M1710 CPU FAN

To engulf a particle or pathogen, a phagocyte extends portions of its plasma membrane, wrapping the membrane around the particle until it is enveloped (i.e. the particle is now inside the cell). Once inside the cell, the invading pathogen is contained inside an endosome which merges with a lysosome.^[3] Compaq Presario CQ42-228LA Laptop Keyboard

The lysosome contains enzymes and acids that kill and digest the particle or organism. Phagocytes generally patrol the body searching for pathogens, but are also able to react to a group of highly specialized molecular signals produced by other cells, called cytokines. The phagocytic cells of the immune system include macrophages, neutrophils, and dendritic cells. HP Pavilion dm1-1010st Laptop Keyboard

Phagocytosis of the hosts’ own cells is common as part of regular tissue development and maintenance. When host cells die, either internally induced by processes involving programmed cell death (also called apoptosis), or caused by cell injury due to a bacterial or viral infection, phagocytic cells are responsible for their removal from the affected site.^[2] DELL 454RX Laptop Keyboard

By helping to remove dead cells preceding growth and development of new healthy cells, phagocytosis is an important part of the healing process following tissue injury.

Macrophages, from the Greek, meaning "large eaters," are large phagocytic leukocytes, SAMSUNG R522 Laptop Keyboard

which are able to move outside of the vascular system by moving across the walls of capillary vessels and entering the areas between cells in pursuit of invading pathogens. In tissues, organ-specific macrophages are differentiated from phagocytic cells present in the blood called monocytes.  Compaq Presario CQ57 Series Laptop Keyboard

Macrophages are the most efficient phagocytes, and can phagocytose substantial numbers of bacteria or other cells or microbes.^[3] The binding of bacterial molecules to receptors on the surface of a macrophage triggers it to engulf and destroy the bacteria through the generation of a “respiratory burst”, causing the release of reactive oxygen species. TOSHIBA Satellite L755D-SP5165RM Laptop Keyboard

Pathogens also stimulate the macrophage to produce chemokines, which summons other cells to the site of infection.

Neutrophils, along with two other cell types; eosinophils and basophils (see below), are known as granulocytes due to the presence of granules in their cytoplasm, or as polymorphonuclear cells (PMNs) due to their distinctive lobed nuclei. SAMSUNG NP-Q320-FS01UK Laptop Keyboard

Neutrophil granules contain a variety of toxic substances that kill or inhibit growth of bacteria and fungi. Similar to macrophages, neutrophils attack pathogens by activating a respiratory burst. The main products of the neutrophil respiratory burst are strong oxidizing agents including hydrogen peroxide, free oxygen radicals and hypochlorite.  HP G42-364LA Laptop Keyboard

Neutrophils are the most abundant type of phagocyte, normally representing 50 to 60% of the total circulating leukocytes, and are usually the first cells to arrive at the site of an infection.^[5] The bone marrow of a normal healthy adult produces more than 100 billion neutrophils per day, and more than 10 times that many per day during acute inflammation.  HP AESP7U00110 Laptop Keyboard

Dendritic cells (DC) are phagocytic cells present in tissues that are in contact with the external environment, mainly the skin (where they are often calledLangerhans cells), and the inner mucosal lining of the nose, lungs, stomach and intestines.^[2] They are named for their resemblance to neuronal dendrites, but dendritic cells are not connected to the nervous system. HP G61-425ES Laptop Keyboard

Dendritic cells are very important in the process of antigen presentation, and serve as a link between the innate and adaptive immune systems.

Basophils and eosinophils are cells related to the neutrophil (see above). When activated by a pathogen encounter, basophils releasinghistamine are important in defense against parasites, and play a role in allergic reactions (such as asthma).^[3] HP 640436-001 Laptop Keyboard

Upon activation, eosinophils secrete a range of highly toxic proteins and free radicals that are highly effective in killing bacteria and parasites, but are also responsible for tissue damage occurring during allergic reactions. Activation and toxin release by eosinophils is therefore tightly regulated to prevent any inappropriate tissue destruction. Lenovo 3000 N200 Laptop Keyboard

Natural killer cells, or NK cells, are a component of the innate immune system which does not directly attack invading microbes. Rather, NK cells destroy compromised host cells, such as tumor cells or virus-infected cells, recognizing such cells by a condition known as "missing self."  DELL XPS 15 L502X Laptop Keyboard

This term describes cells with low levels of a cell-surface marker called MHC I (major histocompatibility complex) - a situation that can arise in viral infections of host cells.^[7] They were named "natural killer" because of the initial notion that they do not require activation in order to kill cells that are "missing self." IBM Lenovo ThinkPad R51 1833 Laptop Keyboard

For many years it was unclear how NK cell recognize tumor cells and infected cells. It is now known that the MHC makeup on the surface of those cells is altered and the NK cells become activated through recognition of "missing self". Normal body cells are not recognized and attacked by NK cells because they express intact self MHC antigens. HP G62-a20EJ Laptop Keyboard

Those MHC antigens are recognized by killer cell immunoglobulin receptors (KIR) which essentially put the breaks on NK cells. The NK-92 cell line does not express KIR and is developed for tumor therapy.

Like other 'unconventional' T cell subsets bearing invariant T cell receptors (TCRs),  ACER Aspire 5742 Laptop Keyboard

such as CD1d-restricted Natural Killer T cells, γδ T cells exhibit characteristics that place them at the border between innate and adaptive immunity. On one hand, γδ T cells may be considered a component of adaptive immunityin that they rearrange TCR genes to produce junctional diversity and develop a memory phenotype. HP Pavilion DV7-3186cl laptop keyboard