Antibody
A Y-shaped protein produced by B-cells of the adaptive immune system. Antibodies recognize specific molecular targets — antigens — and either tag them for clearance or block their function directly.
How researchers study it
Antibodies are produced by B-cells after antigen exposure — through infection or vaccination. The first wave of response is typically IgM. Class switching follows over days to weeks, producing IgG (the most abundant circulating isotype), IgA (mucosal surfaces), and others (Janeway's Immunobiology, NCBI Bookshelf).
Two functional categories matter most for COVID-19 research: binding antibodies and neutralizing antibodies. Binding antibodies detect the presence of antigen — they show up on most clinical antibody tests. Neutralizing antibodies do something stronger: they block the antigen from doing its job. For SARS-CoV-2, neutralizing antibodies bind the spike protein's receptor-binding domain and prevent it from attaching to ACE2 (Khoury et al., Nature Medicine, 2021, PubMed 34002089).
Antibody levels decline over months after infection or vaccination, but B-cell memory persists much longer — meaning even when circulating antibody titers fall, the body can typically generate new antibody quickly on re-exposure. The NIH and CDC have published guidance noting that antibody test results should not be used to determine individual protection — they are population-level research tools.
Common misconceptions
- Janeway's Immunobiology, NCBI Bookshelf. ncbi.nlm.nih.gov/books/NBK27144
- Khoury DS et al. "Neutralizing antibody levels are highly predictive of immune protection from symptomatic SARS-CoV-2 infection." Nature Medicine, 2021. PubMed: 34002089
- CDC. "Antibody Tests for COVID-19." cdc.gov