IgG: definition, role and level of immunoglobulin G

IgG: definition, role and level of immunoglobulin G

Immunoglobulins or Ig are antibodies produced by cells of the immune system, lymphocytes. Immunoglobulins G or IgG, a class of Ig found in blood and interstitial fluid, are responsible for protecting the body and organic tissues in the event of exposure to pathogens responsible for infections ( bacterial, viral, parasitic, etc.).

What does IgG mean?

IgG is the term designating immunoglobulins G, each of which is composed of peptide chains. “This is a type of immunoglobulin. specifies Dr Guillaume Letizia, medical biologist at the Dunkirk hospital center laboratory. “Immunoglobulins are proteins, in particular antibodies involved in the body’s defense against infectious agents, such as bacteria or viruses.” THE IgG therefore have an important role in the body’s defense.

Antibody testing and serology

For example, in pregnant women, immunity against rubella, a virus, or toxoplasmosis, caused by a parasite, is systematically sought. “We look at whether the body has produced antibodies in order to provide advice to patients to protect themselves from infections.”

“When we look at whether IgG are directed against specific infectious agentsIt’s about a serology. We then look at the immune status.”

In all cases, the results are interpreted by a biologist, then by the prescribing doctor.

The different types of IgG antibodies (IgA, IgE, IgM…)

There are different types of immunoglobulins, as Dr Letizia explains to us. “During first contact with an infectious agent, IgM are the first antibodies to be synthesized by lymphocytes (white blood cells). Then, the IgM are replaced by the IgG which persist over the longer term. IgA are antibodies synthesized in the mucous membranes, such as in the intestines or in the respiratory tract. As to IgEthese are antibodies involved in allergic mechanisms“, underlines the biologist.

Why do an IgG test?

The dosage of specific immunoglobulins of the IgM and IgG type is used to observe the patient’s immune status. “We are particularly interested in the quality of his immune system. We look at whether he is immune to certain infectious agents.”

How does a dosage take place?

The dosage of IgG requires no preparation; This is a blood test. It is not necessary to fast. “You must be fasting for a hormonal, glycemic, calcium or fat (triglycerides) measurement, but not to measure IgG.”

IgG or IgM: how to interpret the results (high, low levels, presence of IgG)

The analysis reports are interpreted by biologists and doctors. “Let’s take a common result, that of a pregnant woman not immunized against toxoplasmosis. Her IgM and IgG levels are negative, which means that she is not immune to toxoplasmosis, because she is not has not had an infection either recently (IgM negative) or in previous months or years (IgG negative). She must therefore follow her doctor’s recommendations (avoid contact with cats, wash food thoroughly, etc.) and have a blood test every month to check for infection,” illustrious Dr Letizia.

Each IgG has its specificity. The presence of IgM indicates a recent infection, while that of IgG reveals an old infection, for at least more than a month.

In summary, a negative IgG level reveals an absence of old infection, which means that the patient is not immune. In the case of toxoplasmosis, for example, it is preferable for IgG serology to be positive before pregnancy. Otherwise, preventive measures can prevent the onset of infection during pregnancy.

What is the correct IgG level?

There is no average level for microbe-specific immunoglobulins. For toxoplasmosis testing, we want the IgG level to be high before pregnancy. For Lyme disease serology, we “wish” that the IgG level is negative, to caricature. Clearly, everything depends on the research context (hepatitis C, HIV, etc.)” specifies our specialist.

Who secretes IgG?

THE IgG are secreted by white blood cells and more precisely lymphocytes, key cells in the immune response. “When an infectious agent attacks the body, IgM is first secreted for a few weeks. IgM is secreted into the lymph nodes. Then IgG appears. They are biological markers present in the blood circulation for the rest of life,” specifies the specialist.

Why do a weight test for immunoglobulins?

The weight determination of immunoglobulins measures all the immunoglobulins in the body without looking at their specificity in relation to infectious agents. “If immunodeficiency is suspected, IgG levels may be low. Thus, we suspect a defect in immunity, which does not predict any particular agent. If levels are low, IgG is reduced against all infectious agents. The weight dosage is therefore a global dosage of immunoglobulins“.