Immunoglobulins

Question 1

Different types of immunoglobulins

Answer 1

1. IgG: (2º response)
2. IgA: Secretory
3. IgM: Macro Ig AKA natural antibody (1º response)
4. IgD: ?
5. IgE: anaphylactic hypersensitivity, allergic reactions.

Question 2

IgG

Answer 2

• Human IgG is expressed on the surface of mature B cells.
• IgG are the smallest but most common antibody (75% to 80%) of all the antibodies in the body.
• IgG is the predominate antibody in secondary immune response.
• IgG is the only human immunoglobulin to pass from mother to fetus to transfer immunity.
• IgG can activate complement (along with IgM)
• Binds fragment crystallization (Fc) receptors.

Question 3

IgM

Answer 3

• Human IgM is expressed on the surface of immature and mature B cells as monomers.
• IgM are the largest antibody.
• IgM are the first type of antibody made in response to an infection.
• IgM is the first human immunoglobulin to be made by a fetus and virgin B cells which are challenged with antigen.
• IgM can activate complement (along with IgG)
• Pentameric structure binds fragment crystallization (Fc) receptors.

Question 4

IgA

Answer 4

• IgA is the most prevalent lg _in secretion_s (e.g. tears, saliva and mucous).
• IgA antibodies protect body surfaces that are exposed to outside foreign substances like the nose, breathing passages, digestive tract, ears, eyes, and vagina.
• IgA is secreted in milk so can give passive immunity to infants.
• IgA does not fix complement
• Binds fragment crystallization (Fc) receptors.

Question 5

IgD

Answer 5

• Human IgD is expressed on the surface of mature B cells.
• IgD works with IgM in B cell development.
• IgD antibodies are found in small amounts in the tissues that line the belly or chest
• IgD is found in very low levels in serum
• IgD does not fix complement

Question 6

IgE

Answer 6

• Human IgE is expressed on the surface of mature B cells.
• IgE antibodies are found in the lungs, skin, and mucous membranes.
• IgE mediates anaphylactic hypersensitivity or allergic reactions.
• IgE is the least abundant Ig in the serum
• IgE does not cross placenta or fix complement.
• Fragment crystallization (Fc) receptors for IgE** are found on eosinophils. IgE binds Fc receptors on mast cells and basophils even before interacting with antigen. → involved in allergic reactions*.

* (Allergen is bound to IgE on cells which releases various pharmacological mediators which cause allergies.)