Diagnosis – Primary Immunodeficiency

00:01 So very typically in an infant with primary immunodeficiency, the child will be getting recurrent infections that’ll be quite severe.

00:09 Of course all children get infections but usually one or two days later they’re fit and well and they’re running around again, perfectly healthy.

00:16 But in children with primary immunodeficiencies, they will not recover very well from these infections and the parents maybe will be a bit concerned and they’ll take them along to the doctor’s clinic and eventually they may get investigated if primary immunodeficiency is suspected.

00:35 And there are a number of different tests that can be carried out to try and help in the diagnosis of primary immunodeficiency.

00:42 For example, the number of cells of the immune system can be counted.

00:46 One can look for the number of CD3+ lymphocytes.

00:50 CD3 is a molecule that’s found on the surface of all T-cells, so this will tell you whether there is a T-cell deficiency or not.

00:57 Then one can look a little bit deeper and look at individual subsets of T-cells, for example look at the number of CD4+ cells, the number of CD8+ cells.

01:08 One can also assess the function of cells in vitro.

01:12 For example, you can stimulate T-cells with a mitogenic substance called phytohemagglutinin (PHA), or one can stimulate with specific antigens, one can look for the production of cytokines such as interleukin-2 in vitro in the laboratory.

01:32 One can also look at the function of the immune system within the individual child using delayed hypersensitivity reactions to purified protein derivative (PPD) of Mycobacterium tuberculosis.

01:50 Regarding investigation of B-cell primary immunodeficiencies, again one can enumerate cells.

01:57 There are various molecules that are pretty much restricted to being expressed on B-cells but not other cells of the immune response.

02:05 CD20 is a good example of that.

02:07 One can look at cell surface membrane immunoglobulin, again very characteristic of a B-lymphocyte.

02:14 One can also look at the levels of immunoglobulin that are being secreted into the body of that particular individual.

02:23 Regarding the in vivo functioning, one can look at specific antibody levels.

02:29 So as well as measuring total immunoglobulin levels, you can look at levels of antibody against particular antigens.

02:37 For example, isohemagglutinins, antibodies against E-coli, against tetanus and so forth.

02:43 And one may want to immunize those individuals with non-live vaccines.

02:49 It’s very important that anybody suspected of immunodeficiency is never ever given a live vaccine, but using bacterial toxins; for example tetanus toxin or diphtheria toxin.

02:59 One can look and see whether the response is adequate to help identify if there is a B-cell immunodeficiency.

03:06 Regarding phagocytic cells, one can count the number of circulating neutrophils for example.

03:11 And there’s also a test that one can carry out in vitro called the nitroblue tetrazolium test, which essentially looks at the ability of neutrophils to mount a respiratory burst.

03:22 And in chronic granulomatous disease, there is an inability to mount a respiratory burst, so this test would pick that up.

03:31 And finally, looking at complement deficiencies, one can use a hemolysis assay to look at the ability of serum from the individual to lyse red blood cells, using the membrane attack complex.

03:46 If the membrane attack complex is not able to be produced, that would suggest a complement deficiency.