Anti-SARS-CoV-2 antibody in breast milk: Importance of method for evaluating IgA antibody titer against SARS-CoV-2 variants

Five types of antibodies (IgG, IgM, IgA, IgD, IgE) play a major role in the in vivo immune system. All five antibodies are present in breast milk. The amount of secretory IgA accounts for about 90% of the amount of all antibodies present in breast milk.

Secretory IgA is the most abundant in the first milk secreted within the first few days after delivery. In particular, infant babies have a low ability to make IgA on their own. Therefore, IgA in breast milk is important for preventing infection with SARS-CoV-2.

In this paper, it is found that breast milk contains a large amount of IgA and IgG against SARS-CoV-2 after the second dose of the COVID-19 vaccine. In this respect, the importance of two doses of COVID-19 vaccine was shown.

In preliminary studies, it has already been reported that a single dose of the BNT162b2 vaccine markedly induces neutralized IgG activation against the B.1.1.7 variant in people previously infected with original SARS-CoV-2. However, compared to the method of antibody titers of IgM and IgG against SARS-CoV-2, The method for evaluating the antibody titer of IgA against original SARS-CoV-2 and SARS-CoV-2 variants has not yet made great progress. In particular, it is important to establish a method for evaluating the antibody titer of IgA against SARS-CoV-2 variants, which has been pointed out to have strong infectivity and a high severity rate.

IgA secreted from mucosal cells is abundant in mucus such as nasal mucus, airway mucus, and intestinal mucus, and protects the body from pathogens such as viruses and bacteria. Therefore, IgA is called mucosal immunity. A large amount of IgA is also present in breast milk, which protects infants and newborns from pathogens.

Author contributions
T.H. wrote the manuscript. I.K. carefully reviewed the manuscript and commented on aspects of clinical medicine, shared information on clinical medicine.

Disclosure of potential conflicts of interest
The authors declare no potential conflicts of interest.

Data availability and Consent to publish
This manuscript is an editorial and does not contain research data.
Therefore, there is no research data or information to be published or opened.

Acknowledgments
We thank all the medical staffs and co-medical staffs for providing and helping medical research at National Hospital Organization Kyoto Medical Center.

Doctor specializing in cancer medicine/Cancer genomic medicine/Emerging infectious diseases JAMA Published on April 17, 2021. by Kyoto@Takuma H