Several questions on Infection and Disease

[Irving4Prez]

On a slide from one of our power point's, T helper cells are described to "recognise antigens that are presented on phagocytes (as well as class 2 markers) and stimulate B cells". Through the process of phagocytosis, aren't the pathogens meant to be engulfed and thus eliminated? How is it that B cells are stimulated when they are identified by T helper cells?

Secondly, I can't seem to get my head around the specific functions of B cells. Plasma B Cells produce and secrete large amounts of antibodies in response to the exposure of an antigen but how does this assist in the removal of the pathogen? Furthermore, what occurs when an antibody binds to a non-self antigen?

[Russ]

Phagocytosis will break down the pathogens but it saves little bits of them (that are harmless) to show off to the T cells. When the T cells see them, they recognise there's a problem and they go and provide their own signal to B cells, activating them.

B cells will produce antibodies after activation, which go and bind the pathogen. This can help in removal in several ways. It can bind and physically block an important receptor that the pathogen uses. It can coat the pathogen and make it easier for the rest of the immune system to recognize it. It can help activate other immune cells.

That was the concise version, would you like more detail or is it clearer?

[Irving4Prez]

Are there any other ways in which T cells can identify foreign material? Or will they only recognise there presence when they have been engulfed by a phagocyte?

I know that T helper cells and Cytotoxic cells vary in function but our teacher mentioned cytotoxic cells "kills body cells that have been infected with a virus". At VCE level, do we have to know how they explicitly kill these cells?

On another note, do any of the cells belonging to the immune system have a specific function in the lymphatic system?

Thanks Russ, your reply was clear

[kerry.j]

T cells only have receptors that recognise antigen-MHC complexes, so that's the only way they can identify foreign materials, I think.

Cytotoxic T cells kill virus-infected body cells by secreting enzymes, in a similar way to natural killer cells.

[REBORN]

Cytotoxic T cells release perforin (a protein) which destroys the virus-infected cell

[Yacoubb]

Phagocytosis will break down the pathogens but it saves little bits of them (that are harmless) to show off to the T cells. When the T cells see them, they recognise there's a problem and they go and provide their own signal to B cells, activating them.

B cells will produce antibodies after activation, which go and bind the pathogen. This can help in removal in several ways. It can bind and physically block an important receptor that the pathogen uses. It can coat the pathogen and make it easier for the rest of the immune system to recognize it. It can help activate other immune cells.

That was the concise version, would you like more detail or is it clearer?

I know this post is a bit late but I just want to clarify if my understanding is correct:

When say a macrophage identifies a non-self "foreign" antigen, it binds to it and engulfs it. Lysosomes then release digestive enzymes that break down this foreign antigen; however, some antigen fragments are presented by the antigen-MHC 2 markers to Helper T Cells. Once the helper T cells dock into the MHC-2 marker, the helper T cell is activated. This results in Helper T cells activating specific B-cells which produce specific antibodies, depending upon the detected non-self antigen. This is a humoral response, because the antibodies and macrophages that are also activated during the humoral response, attach to antigens travelling within the extracellular fluid and make it easier for these non-self antigens to be engulfed by phagocytes, macrophages, eosinophils, neutrophils, etc. A cell-mediated response is also initiated as Helper-T cells activate cytotoxic T-cells; these cytotoxic T cells carry out their functions by releasing perforin (a protein) which destroys viral-infected cells (i.e. viruses are obligate intracellular pathogens that can only reproduce and grow when they are within the cells of an organism). Hence, this immune response is called the adaptive, "cell-mediated" response.

Memory B-cells are also produced; if a particular infection is caused by the same antigen that has been detected before and the primary antibody response has produced specific antibodies against the non-self antigen, the memory B-cells would have retained memory of the antigen and thus in the secondary antibody response, more antibodies are produced in a shorter period of time, building up immunity of the organism to the non-self antigen, and allowing the non-self antigen to be destroyed very quickly by the immune system. How do memory T-cells differ?

[simpak]

What you are saying is basically all good.  With respect to memory; a large reason memory works is that you've expanded the number of cells in the population that are responsive to that antigen (via clonal expansion in the beginning) and then those cells are maintained.  So you can imagine, for either B cells or T cells, having more of the cells will allow a quicker response.  You wouldn't need to know anything in detail about why T memory cells would be more effective other than the fact that they are more frequent than the naive cells prior to the initial infection and they are more efficient at clearing the infection.

[MangoPengy]

Hi,
  Sorry for intruding but I had a question about Infection and Disease as well...but I didn't see a reason to start a new thread...so I hope it's okay to post here?


Are 'vectors' necessarily animals (usually insects) or can they just be classified as agents? If the latter, what example can be given?

Also what's the definition for agglutination?

THANKS HEAPS.

[alondouek]

Vectors are biotic factors that carry disease. We call abiotic factors 'vehicles' - such as air, food, soil, etc

Agglutination is the 'clumping' or aggregation of disease particles (or red blood cells in another context) when held together by antibodies. I doubt this is a sufficient definition, but it should give you a starting point

[MangoPengy]

Vectors are biotic factors that carry disease. We call abiotic factors 'vehicles' - such as air, food, soil, etc

Agglutination is the 'clumping' or aggregation of disease particles (or red blood cells in another context) when held together by antibodies. I doubt this is a sufficient definition, but it should give you a starting point

Ahh, I see. Thank-you!