A recent study published in Biological Psychology evaluated whether individuals could assess the strength of their antibody response following coronavirus disease 2019 (COVID-19) vaccination.
Study: Estimation of antibody levels after COVID-19 vaccinations: Preliminary evidence for immune interoception. Image Credit: Corona Borealis Studio/Shutterstock.com
The immune and central nervous (CNS) systems are intrinsically linked, and the CNS connections regulate and orchestrate the functions of the immune system. For instance, the sick feeling during a cold is generated by the immune system communicating with the CNS.
This communication is bidirectional, and CNS signals can influence immune functions. The CNS receives signals from the periphery via the vagus nerve.
While the information route is established, how it affects individuals and whether it is accessible is less understood. Interoceptive signals from the periphery are likely transformed into holistic readout of bodily functions in the insular cortex, through which the brain receives information regarding the state of the immune and other systems. Interoceptive accuracy has been measured mainly at the cardiac level but never at the immune system level.
Although immune interoception has rarely been examined, several studies have evaluated self-rated health (SRH). Interestingly, SRH measures have been reported to predict mortality. Others have reported links between SRH and immune markers.
SRH is shown to be related to health indices and outcomes and might be associated with interoceptive messages and, thereby, with immune interoception.
About the study
In the present study, researchers evaluated whether self-predicted antibody levels correlate with actual levels of antibodies. Healthy volunteers aged 18-59 were recruited. Subjects were excluded if they had chronic illness/COVID-19 history, reported fever, loss of smell/taste, and shortness of breath since 2020, or were vaccinated > 55 days ago.
Cardiac impedance and electrocardiography were recorded. Participants completed several questionnaires, including Beck's depression inventory.
They also rated their psychological and physical health and reported daily average sleep duration, weekly physical activity, smoking and alcohol habits, relationship status, and socioeconomic status.
Subsequently, participants' blood samples were collected, and they were asked to complete a second set of questionnaires on COVID-19 vaccination status, vaccine type, and side effects. They also rated their perceived antibody levels on a scale of 0-10. Participants also provided saliva samples for measuring cortisol levels.
The study included 166 participants with between 136 and 10,938 binding antibody units (BAU)/ml of immunoglobulin G (IgG). All individuals' antibody levels exceeded the positive threshold of 35.2 BAU/ml.
Most participants (134) received the BNT162b2 vaccine, 19 received the mRNA-1273 vaccine, one received the ChAdOx1 vaccine, and 12 received a combination of ChAdOx1 and one of the mRNA vaccines (heterologous vaccination).
The sole ChAdOx1 recipient was excluded from the analysis. Participants with heterologous vaccination exhibited significantly reduced IgG levels than homologous mRNA vaccinees.
Antibody levels were not significantly different between mRNA-1273 and BNT162b2 recipients: participants' age and the time since the last vaccination were associated with lower IgG levels. Further, antibody levels were positively associated with body mass index (BMI).
The measured antibody levels significantly correlated with self-predicted (i.e., perceived) levels of antibodies and feelings of protection against COVID-19.
The daily average sleep duration, physical activity, perceived psychological and physical health, and high-frequency heart rate variability (HF-HRV) were not predictive of antibody levels. Besides, perceived antibody levels and feelings of protection were associated with perceived psychological health.
Depression scores were significantly associated with perceived antibody levels. The daily average sleep duration was significantly associated with feelings of protection. HF-HRV was not related to perceived antibody levels or feelings of protection. Perceived psychological health and average sleep duration were unrelated.
Participants' self-predicted antibody levels and feelings of protection from COVID-19 were positively correlated with actual IgG titers.
Of note, subjects who rated their antibody levels or feelings of protection against COVID-19 below six had lower antibody titers, suggesting that those who perceived having lower antibodies showed below-average antibody titers (for their BMI and age).
Almost all individuals with significantly above-average antibody titers rated themselves as having high antibody levels, suggesting that individuals at the extremes of IgG levels appeared to have a sense of their antibody levels.
The authors speculate that participants perceived as being less protected or having reduced antibody levels likely had an interoceptive sense of poor immune health.