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The immune system

the immune system

Your immune system is your body’s protection against disease. HIV damages immune cells called CD4 cells. If HIV is not treated, your immune system is weakened. A weak immune system can’t fight off infections and you will become ill.

What is the immune system?

The immune system is the body’s mechanism for protecting itself against the many harmful organisms which try to invade it, such as bacteria and viruses.

It's a highly complex network of tissues, organs and cells, including blood cells.

How does the immune system work?

When an organism gets inside your body (for example, when you breathe in the common cold virus), white blood cells that form part of your immune system go to investigate.

These white blood cells have different roles and work together. One group - the T-cells - co-ordinate the immune response, and other group - the B cells - produce antibodies to fight the problem.

Some T-cells have a protein on their surface called CD4 which is why we often refer to these as CD4 cells.

What does HIV do to my immune system?

HIV is dangerous because the virus destroys the very cells of your immune system that are supposed to be keeping you well: the CD4 cells.

the HIV life cycle

HIV attaches itself to a CD4 cell and enters it. Then it makes copies of itself inside the CD4 cell and goes on to damage and destroy the cell. New copies of HIV burst out of the CD4 cell and go off to find more cells to invade.

If the number of CD4 cells (the CD4 count) is reduced, the immune system has fewer cells to help it defend the body from other organisms. This means you're at a greater risk of getting ill.

The immune system does try to fight HIV infection: it produces antibodies that try to fight off the antigens which are a part of the invading organism – in this case HIV. The body will try to mount an attack but for various reasons in the case of HIV it’s unable to eradicate the virus.

How does this affect my health?

Normally the body's immune system would fight off an infection, but HIV prevents it from working properly.

However, effective HIV medication can keep the virus under control, stop you passing on the virus and enable you to live a normal lifespan.

More about HIV:

Next: Viral load and CD4 count ››

‹‹ Previous: HIV transmission



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The Information Standard: Certified member

This article was last reviewed on 14/6/2017 by Anna Peters

Date due for the next review: 14/6/2020

Content Author: S. Corkery (NAM)

Current Owner: Kerri Virani

More information:

National Institute of Allergy and Infectious Diseases, HIV/AIDS

Overview of HIV and the immune system, NAM Aidsmap

How the immune system works, NAM Aidsmap

Why HIV Antibodies are Ineffective at Blocking HIV, Science Daily, April 2009

What an HIV vaccine would have to do, NAM Aidsmap

Sexual Activity Without Condoms and Risk of HIV Transmission in Serodifferent Couples When the HIV-Positive Partner Is Using Suppressive Antiretroviral Therapy, Journal of the American Medical Association: Alison J. Rodger, MD; Valentina Cambiano, PhD; Tina Bruun, RN; Pietro Vernazza, MD; Simon Collins; Jan van Lunzen, PhD; Giulio Maria Corbelli; Vicente Estrada, MD; Anna Maria Geretti, MD; Apostolos Beloukas, PhD; David Asboe, FRCP; Pompeyo Viciana, MD1; Félix Gutiérrez, MD; Bonaventura Clotet, PhD; Christian Pradier, MD; Jan Gerstoft, MD; Rainer Weber, MD; Katarina Westling, MD; Gilles Wandeler, MD; Jan M. Prins, PhD; Armin Rieger, MD; Marcel Stoeckle, MD; Tim Kümmerle, PhD; Teresa Bini, MD; Adriana Ammassari, MD; Richard Gilson, MD; Ivanka Krznaric, PhD; Matti Ristola, PhD; Robert Zangerle, MD; Pia Handberg, RN; Antonio Antela, PhD; Sris Allan, FRCP; Andrew N. Phillips, PhD; Jens Lundgren, MD
JAMA. 2016;316(2):171-181. doi:10.1001/jama.2016.5148

START trial finds that early treatment improves outcomes for people with HIV, by Gus Cairns, NAM Aidsmap, May 2015

What is the life expectancy for someone with HIV?, NHS Choices, May 2015

Understanding the Immune System, The Well Project, June 2016

Understanding CD4 cells and CD4 tests, The Well Project, June 2016

Cells of the immune system, NAM Aidsmap

Receptors and co-receptors and immunity to HIV, NAM Aidsmap

HIV: cell binding and entry, by Craig B. Wilen, John C. Tilton, Robert W. Doms, Perspectives in medicine, April 2012

The HIV lifecycle, NAM Aidsmap

HIV lifecycle by Michael Carter, NAM Aidsmap, April 2014

What is a normal CD4 count, CD4% and CD4:CD8 ratio?, by Simon Collins, iBase, 12 December 2016

Antibody-antigen complex, Microbiology online, 2017

What are HIV and AIDS?, Avert, March 2017

How HIV infects the body and the lifecycle of HIV, Avert, April 2017

National Institute of Allergy and Infectious Diseases – Immune System Disorders:

National Institute of Allergy and Infectious Diseases - Overview of the Immune System:

NHS Choices – HIV and AIDS: Causes