Question

What is the best immunological assay for each of the following situations? For each situation, name the assay, describe how it works, and why it is appropriate. Assume in both cases that any type of specific antibody needed for the assay you propose is available.

a. Determine the number of memory T cells and naïve T cells based on the level of CD45RA present on the surface of the T cells.

b. Determine the level of IgG specific to measles in the blood of a person who has not been immunized but may have been exposed.

Answer 1

1)In the peripheral blood of patients with tuberculosis a novel human effector/memory CD4+ T cell subset with a non-classical, naive-like T cell phenotypes is identified . These cells were CD45RO−, CD45RA+, CCR7+, CD62L+, CD27+, and capable of rapidly secreting multiple cytokines (IFN-γ, TNF-α, IL-2) in response to different M. tuberculosisantigens . We have designated this CD4+T cell population as TCNP cells (T cells that are able to produce cytokines with a naive phenotype). TCNP cells were further phenotyped as CD95lo CD28int CD49dhiCXCR3hi and a sizeable fraction (ranging from 50 to 80%) also expressed CD31. Following curative tuberculosis treatment, the size of this T cell subset significantly decreased, suggesting that these cells are markers of active tuberculosis disease during infection with M. tuberculosis and probably expand in response to actively multiplying bacilli. Accordingly, subjects with latent M. tuberculosis infection had a lower proportion of responding CD4+ TCNP cells in the peripheral blood, than tuberculosis patients.

Compared to TSCM cells, TCNP cells express higher levels of CD49d and comparable levels of CXCR3, but they do not express CD95 . The α4 integrin CD49d associates with β-integrin subunits to form α4β7 or α4β1 heterodimers that regulate the trafficking of effector memory T cells to inflamed tissues. Similarly, CXCR3 regulates lymphocyte trafficking in response to its ligands as above reported. Therefore, it is likely that CD4+ TCNP cells may be able to rapidly traffic to sites of M. tuberculosisinfection .

2)Laboratory evidence of immunity is based on testing to detect measles IgG. People who have negative or equivocal results for measles IgG should be vaccinated or revaccinated. In some cases vaccination is not possible, and testing with a second line diagnostic assay may be necessary to determine the patient’s immune status. CDC has evaluated the performance of several of the assays used to detect measles IgG. Some of the commercial, manually-processed enzyme immunoassays (ELISAs) are slightly more sensitive than high-throughput automated IgG test platforms that are typically used by large commercial laboratories.

Your body makes two rubella antibodies: IgM and IgG. If IgM is found in your blood, you may have had a recent infection. If IgG is present, it could mean that you had a rubella infection in the past or that you had a vaccine. These antibodies mean that you have the protection you need.  

The findings for rubella antibody are given in ratio form:

• HAI less than 1:8, means you have no immunity to rubella

• HAI greater than 1:20, means you have immunity to rubella

Findings for measles antibody:

• If IgM antibodies are present, it may mean you have an active measles infection.

If you have IgG antibodies in your blood but no IgM antibodies, it could mean that you are immune to measles or had the infection previously.

Findings for mumps:

• If antibodies are found, it may mean that you have an active mumps infection or immunity to mumps.