2.4b Immune Responses: Phagocytosis, Cell-Mediated, Humoral

How do the plasma cells cause the death of the pathogen?

They produce antibodies, which cause agglutination (the pathogens to clump together) and act as markers so that phagocytes can locate and destroy them by phagocytosis.

Why do phagocytes then become APCs themselves?

They start to present antigens of the pathogen they've engulfed on their own surface. This is because it attracts lymphocytes so that the specific immune responses of cell-mediated and humoral response can begin, to ensure long-term immunity.

What type of cell carries out phagocytosis?

a type of white blood cell called Phagocytes

Give five kinds of cell a T-lymphocyte would respond to?

pathogens, toxins, phagocytes that are antigen presenting, cancer cells, foreign cells, host cells of viruses

Name some physical lines of defence.

skin, mucus + cilia, tears, stomach acid, scabs, earwax

Why might several types of B cell be cloned?

A pathogen may have several different types of antigen on its surface. Also, some pathogens produce toxins, such as the cholera bacterium. These toxins also act as antigens of their own so yet more B cells are cloned.

Why is humoral immunity called that?

Because B cells detect antigesn present in the bodily and tissue fluids like the blood. These used to be called humours. Humoral immunity involves antibodies which are proteins that dissolve in these fluids.

Why do we call the plasma cell response the primary immune response?

Because it is the first immune response, the destruction of pathogens. It is the immediate primary threat that they are getting rid of.

Why is the T-Lymphocytes response called the cell-mediated or cellular response?

Because they detect antigens present on the surface of body cells.

Why is cell-mediated immunity effective on viruses?

Because viruses live inside a host body cell. The T cells can detect antigens on these host body cells and kill them, sacrificing the body cell to destroy the virus.

Describe how the B cell attaches to the antigen.

Every B cell produces one type of antibody. There are over 10 million B cells. When the right B cell is located, the antibody that it produces will attach to the antigen on the pathogen because they are complementary. This forms an antibody-antigen complex.

Name and describe the four types of T-Lymphocyte.

Helper T cells - detect and recognize, then divide into other types of cell Cytotoxic T cells - kill pathogens Killer T cells - kill pathogens Memory T cells - can divide rapidly into any other type of T cell if a known pathogen is detected

What type of cell is involved with specific immune responses?

Lymphocytes

Describe how phagocytes kill the pathogen, and what can happen next.

Lysosomes in the phagocyte migrate around the phagosome. They release lysozymes which are powerful digestive enzymes that hydrolyse the pathogen and break it down into small, soluble bits of debris. This debris is then absorbed into the cytoplasm. The phagocyte may then start to present the antigens of the pathogen on it own surface, becoming an APC.

How long do memory cells live for? What do they do in this time?

Many years, even decades. They don't produce any antibodies but they circulate in the blood stream and if they collide with the pathogen again in case of re-infection, they can produce a quick immune response.

How are B cells activated?

Once the B cell is presenting the antigen, a Helper T cell will come along and attach to the antigen. This activates the B cell so that it can start dividing.

Name the three types of immune response and whether they are specific or not.

Phagocytosis - non-specific Cell-medicated immunity - specific Humoral immunity - specific

How long do plasma cells live? what do they do in this time?

Plasma cells only live for a few days but in this time they produce and secrete a huge amount of antibodies very quickly, around 2000 per second.

What are the two types of lymphocyte? Describe the differences between them

T-lymphocytes - these are matured in the thymus gland and involved in cell-mediated immunity. B-lymphocytes - these are matured in the bone marrow and involved in humoral immunity.

How do cytotoxic T cells kill pathogens?

TC cells produce a protein called perforin which makes holes in the cell membrane of the infected cell or pathogen. This makes the membrane totally permeable so it swells up and lysis occurs, and it dies.

What happens after the B cell attaches to the antigen?

The B cell is attached to the antigen by the antibody-antigen complex. The antigen is then taken inside the B cell by endocytosis. The B cell starts to present this antigen on its own surface.

What happens once B cells are activated?

The B cell starts to divide into one of two types of cell - a plasma cell or a memory cell. The plasma cells clone themselves.

Describe how the T-lymphocyte recognizes the pathogen, and what happens next.

The Helper-T cell is the one which detects the pathogen. It has receptors on its surface. One TH cell will have exactly the right receptor to fit the antigen on the infected cell. Once this correct TH cell is located, it will divide rapidly to produce a clone of itself.

Compare the primary and secondary immune response in terms of antibody production.

The antibodies are produced faster and in a much higher volume the second time around, so you don actually become ill again.

How do B cells ensure long-term immunity to a disease?

The memory cells remain in the blood stream for a long time. If the pathogen re-enters the body, these memory cells will recognize it and can divide quickly into the plasma cells which make the correct antibodies. The antibody production the second time is much faster and in a much higher volume so the pathogen is destroyed before it causes symptoms or makes you infectious.

Describe how the phagocytes find the anti-self material.

The pathogen produces chemicals and these act as an attractant for the phagocyte. They may also be attracted by lymphocytes which act as markers.

Describe how phagocytes take in the pathogen.

The phagocyte engulfs the pathogen in a vesicle called a phagosome which then moves inside the phagocyte itself.

When are B lymphocytes produced and what for?

The production of B lymphocytes is stimulated by the T Helper cells, in order to produce the next level of immunity which is humoral immunity.

What kind of immune response are the memory cells responsible for?

The secondary immune response - the response to the secondary, non-immediate, potential threat in the future.

Where are lymphocytes made and what are they like?

They are made in the bone marrow. They mature in the bone marrow or thymus gland. They circulate ion the lymphatic system which involves lymph nodes. There are over ten million types of each lymphocyte so at least one will fit a pathogen.

What four things do helper-T cells do?

They divide to produce cytotoxic T cells which kill the pathogens. They activate B lymphocytes so antibodies are produced. They stimulate phagocyte production so pathogens can be destroyed by phagocytosis. They divide into memory T cells for long-term immunity.