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19.1: Introduction to the Lymphatic and Immune Systems

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  • Chapter Learning Objectives:

    After studying this chapter, you will be able to:

    • Explain the location, structure, and function of the components of the lymphatic system
    • Discuss the integration of the lymphatic system with other body systems
    • Explain how the structure and organization of lymphatic vessels and lymph nodes are suited to their functions
    • Describe the temporal organization of the immune system
    • Distinguish primary and secondary adaptive immune responses

    Rather than being made up of a distinct set of organs like most body systems, the immune system is integrated within each of the body's systems to prevent or slow infection, fight sickness, and rid the body of debris and abnormal cells. The immune system is made up of a combination of anatomical and physiological barriers and specialized cells, including the white blood cells and their derivatives, as well as proteins and other molecules. The lymphatic system is comprised of a distinct set of organs and tissues whose primary functions support the immune system.


    Immune System: HIV and AIDS

    In June 1981, the Centers for Disease Control and Prevention (CDC), in Atlanta, Georgia, published a report of an unusual cluster of five patients in Los Angeles, California. All five were diagnosed with a rare pneumonia caused by a fungus called Pneumocystis jirovecii (formerly known as Pneumocystis carinii). Why was this unusual? Although commonly found in the lungs of healthy individuals, this fungus is an opportunistic pathogen that causes disease in individuals with suppressed or underdeveloped immune systems. The very young, whose immune systems have yet to mature, and the elderly, whose immune systems have declined with age, are particularly susceptible. The five patients from LA, though, were between 29 and 36 years of age and should have been in the prime of their lives, immunologically speaking. What could be going on?

    A few days later, a cluster of eight cases was reported in New York City, also involving young patients, this time exhibiting a rare form of skin cancer known as Kaposi’s sarcoma. This cancer of the cells that line the blood and lymphatic vessels was previously observed as a relatively innocuous disease of the elderly. The disease that doctors saw in 1981 was frighteningly more severe, with multiple, fast-growing lesions that spread to all parts of the body, including the trunk and face. Could the immune systems of these young patients have been compromised in some way? Indeed, when they were tested, they exhibited extremely low numbers of a specific type of white blood cell in their bloodstreams, indicating that they had somehow lost a major part of the immune system. Acquired immune deficiency syndrome, or AIDS, turned out to be a new disease caused by the previously unknown human immunodeficiency virus (HIV), a virus that is transmitted sexually or by contact with infected blood.

    HIV infection had a grim prognosis in the early years. The first treatment was approved in 1987, but had limited efficacy in the long term. Additional anti-retroviral drugs (ARDs, targeting HIV as an RNA virus) were developed over the next ten years and eventually treatment with a combination of anti-HIV drugs termed "highly active antiretrovirals" (HAART) was approved in 1996, reportedly reducing HIV deaths by 60 to 80% in those with access to the treatment. HIV infection is now a chronic, manageable disease for those with adequate access to healthcare. As of the 30th anniversary of World AIDS Day in 2018, treatment can suppress HIV virus levels to below detectable limits with minimal risk of transmitting the virus to a partner. ARDs are now approved for pre-exposure prophylactic (PrEP) use to prevent infection in those that are HIV-negative but at elevated risk of contracting the virus.

    Along with all this progress, the epidemic has highlighted global inequities in access to healthcare. Worldwide, as of 2018, it was estimated that 25% of those living with HIV do not know they are infected with HIV. Learn more about why the HIV epidemic is not over.

    Scanning electron micrograph of HIV virions budding from a white blood cell.
    Figure \(\PageIndex{1}\): HIV Virus. In this scanning electron micrograph, HIV virions (green particles) are budding off the surface of a cultured lymphocyte (pink structure). (Image credit: "HIV Budding Color" by C. Goldsmith is in the Public Domain)


    Why the HIV Epidemic Is Not Over.” World Health Organization, World Health Organization. 28 Nov 2018. [Accessed 15 Dec 2020]

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