Even eight months into the COVID-19 pandemic, scientists are still seeking to understand the clinical and laboratory characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The COVID-19 disease continues to perplex many, as it diverges from current knowledge about viral infections in many ways.
A recent case study published in the Journal of Applied Laboratory Medicine in August 2020 illustrates this with its finding of persistent seronegativity in a patient confirmed to be SARS-CoV-2 positive.
transmission electron microscope image shows SARS-CoV-2—also known as 2019-nCoV, the virus that causes COVID-19—isolated from a patient in the U.S. Virus particles are shown emerging from the surface of cells cultured in the lab. The spikes on the outer edge of the virus particles give coronaviruses their name, crown-like. Image captured and colorized at NIAID's Rocky Mountain Laboratories (RML) in Hamilton, Montana. Credit: NIAID
The index patient was a 49-year-old male, with a history of COVID-like symptoms, who presented after seven days and with a positive history of contact with a COVID-19 case. The patient was on treatment with the drug venetoclax for chronic lymphocytic leukemia. He also had uncontrolled insulin-dependent diabetes mellitus type 2 and had recently discontinued insulin.
The patient was afebrile on admission, with 95% oxygen saturation on nasal oxygen. The chest findings showed nonspecific pneumonia with atypical features. The blood tests showed low white cell counts, lymphopenia, low platelets, and very high glucose levels. The inflammatory markers procalcitonin and C-reactive protein were both high, as was his ESR.
His serum IgG concentration was near the lower limit of normal, and he tested negative for influenza A and B, as well as the respiratory syncytial virus. Once the diagnosis was confirmed, the patient was administered hydroxychloroquine, doxycycline, and insulin.
On the second day, the patient developed hypoxia on nasal oxygen, and cardiac arrhythmias, so that treatment with hydroxychloroquine and venetoclax were both stopped. The deterioration in oxygen saturation continued on day 5, and the patient was admitted to the intensive care unit and intubated for mechanical ventilation.
The patient continued to show clinical worsening, and acute renal failure set in. All through the period of hospitalization, the patient remained positive for the virus.
No Antibody Detected
The residual blood specimens were used for antibody assay verification, but surprisingly, the test turned out negative from the first specimen, taken one week from the onset of symptoms to the last specimen 44 days later. Weekly specimens were tested in these six weeks.
Antibodies typically begin to develop at 6-10 days from infection, first IgM at about 12 days, lasting for up to 35 days at adequate levels. After this, there is a rapid drop in antibody levels. IgG begins to develop at 2 weeks from symptom onset, and peaks at about 17 days from infection. These can be detected at up to 49 days.
The prolonged period of antibody negativity after symptom onset rules out a false negative result due to testing at the wrong time. Moreover, the antigens and assay formats may affect the detection, for which reason the researchers used three assays with a range of antigens and formats. This included the nucleocapsid antigen and the spike antigen.
CLL And Immunodeficiency
The common type of leukemia in adults is chronic lymphocytic leukemia (CLL), and this is linked to a severe reduction in immune function, reflected in repeated infections. This is chiefly seen as a profound deficiency of immunoglobulins, but also an impaired innate immune response.
The tumor also suppresses normal anti-cancer immunity, with overactive Treg cells and failure of T cell and NK cell function. The underlying reason is thought to be tumor cells creeping in among the immune cells, with both types of cells ‘talking’ to each other through cytokines. The net effect is that the tumor grows while the immune reaction is suppressed. This immunodeficiency is exacerbated by the treatment for CLL, tending to increase the number of infections.
Thus, this patient already had impaired immunity at the time of COVID-19 diagnosis. The failure to seroconvert is probably related to the presence of hypogammaglobulinemia in CLL. This could be due to impaired T cell function as well as B cell suppression because of the inhibition of the signaling pathway needed for lymphocytes to differentiate normally. Other factors include TGF-β secretion causing B cells to stop proliferating and increasing IL-2 receptors, thus reducing T cell function and causing a lack of IL-2 in the body.
Thus, there is an imbalance of T cell/B cell interactions, which cause immunodeficiency in CLL, particularly a low level of IgG. As a result of this chronic impairment of immunity, the patient either did not develop specific antibodies or produced only undetectable levels of antibodies.
Similar results have been reported with other serologic tests for hepatitis C and hepatitis E. In fact, one of the COVID-19 serologic assays states the latter as being a limitation of its testing in immunocompromised patients. This mandates the use of viral RNA testing in such patients who have been exposed and have negative serology.
- Lianna Goetz, Jianbo Yang, Wallace Greene, Yusheng Zhu, PhD, A COVID-19 patient with repeatedly undetectable SARS-CoV-2 antibodies, The Journal of Applied Laboratory Medicine, , jfaa137, https://doi.org/10.1093/jalm/jfaa137