3 Laboratory investigation
Last week, you measured the levels of IgG antibodies against SARS-CoV2 spike protein in a group of 30 individuals in order to assess the level of immunity in the population. This week, you are going to take that investigation one step further. Recall that the antibodies against spike protein could be due to vaccination or natural infection. But how could one specifically identify who had been infected?
If a person has been infected they produce antibodies against all structural components of the virus, including the nucleocapsid. Antibodies against the nucleocapsid are called N-antibodies, to distinguish them from the S-antibodies that recognise spike protein.
Activity 3 Measuring N-antibodies by ELISA
Go back to the data in Table 2 [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] that you produced in Week 4. It should contain your own data on S-antibodies in the samples that you measured. You may have downloaded the table instead, which you can download again if you need to: Table 2.
Now identify those individuals who have a titre of S-antibodies >8. You are going to retest these samples to see if they also have N-antibodies.
Now go to the virtual ELISA: epidemiology laboratory, and measure the titre of IgG antibodies against nucleocapsid.
You should carry out the assay in exactly the same way as previously except at step 3 of the assay, you should choose the nucleocapsid ELISA plate (Figure 5)
The standard has IgG N-antibodies (titre = 800) which should be used as a positive control, and the negative control serum has no significant N-antibodies (titre