The Immune System of Human and Macrophages

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The Immune System of Human and Macrophages

The immune system of human beings serves as a shield against different microorganisms. Bacterial infections continually assail the body and it is the agents of the innate immune system that are responsible for immediate attacks on these microorganisms and serve as the first line of defense. These agents are called the Macrophages and the Neutrophils. Macrophages (Greek: big eaters, from makros large + phagein eat) are white blood cells within tissues, produced by the division of monocytes. (Krombach et al 1997, 12613) These cells play a vital role in the immune system as they are responsible for carrying out immune responses by removing unwanted pathogens in the body. According to Petit and Unanue (1974) bacterial recognition by macrophages plays a vital role on the resistance of human being to infection. Another reason why macrophages are crucial to the immune system is that adaptive immune response takes several days before initial responses are carried out and until then the cells of the innate immune system are responsible for safeguarding the human body.

Microbes enter the body through the epithelial layer, or the skin. As soon as they enter, the innate immune response senses the unwanted pathogens and activates the Phagocytic Macrophages in response. The defense mechanism of Macrophages work by first identifying the pathogen, this is done through the use of surface receptors. These surface receptors bind to molecules commonly found in bacteria. Once identified as bacterium, the macrophage initiates engulfment of the cell. The macrophage&attacks the cells present in the local area in which it was activated (New Scientist 1988) And according to Weigle, Dixon and Roberts, (1957) The idea that macrophages took up the antigen and perhaps processed it was already clear by 1956. Macrophages dont take up their own antigens so they have to generate an immune response that will, in order to do so macrophages secrete molecules called cytokines and chemokines. According to Parham (2001), Cytokines are cell behavior-changing proteins produced by macrophages. While chemokines are another set of proteins that are responsible for attracting white blood cells, such as neutrophils, from the bloodstream. These two proteins released by the macrophages are responsible for the process called inflammation.

As simple as it sounds, the innate immune response is one of the greatest defenses the body has against microbial infection. According to Butcher and Picker (1996), One of the more critical roles of the innate immune response is hastening the activation of adaptive immunity. When inflammation occurs it triggers an increase in the activity of the lymphoid tissues. Meanwhile, cells that have been successfully infected by microbes that escaped the initial innate immune response send out signals that activate the lymphocytes and so begin the adaptive immune response.

A good example of the role of the innate immune response is if a person contracts a bacterial infection like syphilis (Treponema pallidum). As soon as the bacterial agents enter the bloodstream they are immediately attacked by macrophages. But if the immune system is so weakened it is unable to neutralize all the bacteria, inflammation soon occurs and the action of macrophages starts a chain reaction that activates the adaptive immune response. Due to the adaptive immune response begun by the macrophages, as soon as the infection is over, the body gains immunity to syphilis.

The innate immune response depends on receptors that recognize the features of common pathogens and it is the reason why the innate immune response is such a critical component of the immune system. Unfortunately, they are overcome easily by most pathogens and the protection rendered can only do so much. For this reason, the innate immune response leads to adaptive immunity. Adaptive immunity is a reinforced version of the innate immune system that provides recognition and enhanced protection against pathogens that have previously infected the body. Unlike innate immune response, the adaptive response serves as long-term protection with immunological memory. But we must remember that the innate response is the reason for the activation of the adaptive response.

Bibliography

Krombach F, Münzing S, Allmeling AM, Gerlach JT, Behr J, Dörger M (1997). The cell size of alveolar macrophages: an interspecies comparison. Environ. Health Perspect, 12613.

New Scientist (1988) The human immune system: The lymphocyte story.

Dixon, F.J., Weigle, W.O. & Roberts, J.C. (1957) Comparison of antibody responses associated with the transfer of rabbit lymph-node, peritoneal exudate, and thymus cells. Journal of Immunology. 78, pp. 56-62.

Petit, J.C. & Unanue, E.R. (1974) Effects of bacterial products on lymphocytes and macrophages: their possible role in natural resistance to listeria infection in mice. Journal of Immunology. 113, pp 984-992.

Parham P (2001) The Immune System. New York/London: Garland Publishing/Elsevier Science Ltd.

EC. Butcher and LJ. Picker. (1996). Lymphocyte homing and homeostasis. Science 272: 60-66.

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