Adaptive immune defenses

3 July 2009

adaptive-immune-systemThe immune response to viral infection comprises innate and adaptive defenses. The innate response, which we have discussed previously, functions continuously in a normal host without exposure to any virus. Most viral infections are controlled by the innate immune system. However, if viral replication outpaces innate defenses, the adaptive response must be mobilized.

The adaptive defense consists of antibodies and lymphocytes, often called the humoral response and the cell mediated response. The term ‘adaptive’ refers to the differentiation of self from non-self, and the tailoring of the response to the particular foreign invader. The ability to shape the response in a virus-specific manner depends upon communication between the innate and adaptive systems. This communication is carried out by cytokines that bind to cells, and by cell-cell interactions between dendritic cells and lymphocytes in lymph nodes. This interaction is so crucial that the adaptive response cannot occur without an innate immune system.

The cells of the adaptive immune system are lymphocytes – B cells and T cells. B cells, which are derived from the bone marrow, become the cells that produce antibodies. T cells, which mature in the thymus, differentiate into cells that either participate in lymphocyte maturation, or kill virus-infected cells.

Both humoral and cell mediated responses are essential for antiviral defense. The contribution of each varies, depending on the virus and the host. Antibodies generally bind to virus particles in the blood and at mucosal surfaces, thereby blocking the spread of infection. In contrast, T cells recognize and kill infected cells.

A key feature of the adaptive immune system is memory. Repeat infections by the same virus are met immediately with a strong and specific response that usually effectively stops the infection with less reliance on the innate system. When we say we are immune to infection with a virus, we are talking about immune memory. Vaccines protect us against infection because of immune memory. The first adaptive response against a virus – called the primary response – often takes days to mature. In contrast, a memory response develops within hours of infection. Memory is maintained by a subset of B and T lymphocytes called memory cells which survive for years in the body. Memory cells remain ready to respond rapidly and efficiently to a subsequent encounter with a pathogen. This so-called secondary response is often stronger than the primary response to infection. Consequently, childhood infections protect adults, and immunity conferred by vaccination can last for years.

The nature of the adaptive immune response can clearly determine whether a virus infection is cleared or causes damage to the host. However, an uncontrolled or inappropriate adaptive response can also be damaging. A complete understanding of how viruses cause cause disease requires an appreciation of the adaptive immune response, a subject we’ll take on over the coming weeks.

  • mdubuque

    What exactly is “remembered” here? Since every viral particle is different, it would seem that the adaptive system needs to remember “similarities” and not just individual signatures.

    In other words, they seem to have somehow classified viruses by serial homology, in my view.

    Are there disadvantages to having too broad of spectrum of “memory” in different aspects of the adaptive system? How is that memory “tuned” and “modulated”?

    I remain intriuged by the notion that all this coding and “memory” in viral systems can be informed by the debate on mathematical linguistics.

    Matt Dubuque

  • http://www.virology.ws profvrr

    What is 'remembered' is conserved protein sequences that bind
    antibodies (in the case of B cell memory, for example). Every particle
    is not antigenically different – the genome is different but that does
    not always translate into different protein. When differences emerge
    in antigenic sites, that's when antigenic drift occurs, and antibodies
    no longer neutralize the virus. More on this to come.

  • http://www.virology.ws profvrr

    What is 'remembered' is conserved protein sequences that bind
    antibodies (in the case of B cell memory, for example). Every particle
    is not antigenically different – the genome is different but that does
    not always translate into different protein. When differences emerge
    in antigenic sites, that's when antigenic drift occurs, and antibodies
    no longer neutralize the virus. More on this to come.

  • Pingback: Adaptive immune defenses: Antibodies

  • Pingback: The complement system

  • Pingback: תאים קפיטליסטים חזיריים ומאבטחים בשכר מינימום | מגירה 2.0

  • Nasir Hussain

    nice post

  • Pingback: Gut microbes influence defense against influenza

  • http://www.prlog.org/11289974-phone-number-lookup-verizon-phone-number-reverse-lookup-to-get-information-you-need-quickly.html reverse phone lookup

    Looks like you’ve done your research very well.

  • Aderonke

    lets say, a persons with multiple myeloma cannot make antibodies. These individuals are still able to clear viral infections from their body using their adaptive immune response. How is this possible?

  • http://www.virology.ws profvrr

    It’s possible that clearance of this particular virus is dependent on cellular responses – such as cytotoxic T cells.

  • Herman512

    i think is important informationa dn people sould be treated and matters with peace
    herman dhoot wolverhampton

  • Pingback: Antibodies Are Not Required for Immunity Against Some Viruses – Science Daily | The Refusers

  • Pingback: More evidence for mild influenza H5N1 infections

  • Adnan zaman

    very clear and well written..

  • Susan Dawson

    Hallo,
    Please can you help. I have a low immune response to bacterial and viral infections which has responded well to both hib and prevanar vaccination. However I still have a low white blood cell response for which my GP has requested a blood test for lymphocyte sub sets.

    I have constant viral cold symptoms which are very debilitating and restrict my work capability and home life. Please can you advise if there is any treatment for such low immunity and perhaps comment on how this condition may have originated.
    With very grateful thanks,
    Susan Dawson.

  • Pingback: Through Arid Places: Seek and Destroy « Invisible Ink

  • http://www.ct-demo2.com/ Buy Oranges

    I’ve been browsing online more than three hours these days, yet I by no means found any interesting article like yours. It抯 lovely value enough for me. In my view, if all webmasters and bloggers made just right content material as you did, the web will be much more helpful than ever before.