Testing for high levels of an enzyme phosphorylation in fresh B cells can rapidly distinguish a specific immunodeficiency syndrome from other primary immunodeficiencies that have similar symptoms.
People with a rare immune deficiency known as activated PI3K-delta syndrome (APDS) have abnormal proliferation of white blood cells and reduced immune function. This leads to recurrent infections, nodular lymph nodes, and antibody deficiency. APDS is a rare disease that is difficult to diagnose, partly because it is so uncommon, but also because its symptoms can be confused with other primary immune deficiencies. It is typically diagnosed by genetic analyses that identify mutations in its known causative genes. But processing the test results can take up to a month.
For people with APDS, their white blood cells, called B lymphocytes, have enhanced phosphorylation of an enzyme called AKT, which is involved in cell survival, growth, proliferation and migration. Previous studies had shown that enhanced phosphorylation of AKT (pAKT) also occurred in T lymphocytes, but first these had to be activated; a process that can take several days.
A new technique now improves the testing process. “Enhanced pAKT in fresh B cells enabled us to establish a rapid diagnostic test using flow cytometry,” says paediatrician Satoshi Okada of Hiroshima University Graduate School of Biomedical and Health Sciences.
APDS is caused by genetic mutations that lead to the hyperactivation of an enzyme called phosphoinositide 3-kinase (PI3K). This, in turn, ultimately leads to the enhanced recruitment of the enzyme AKT to the plasma membrane of white blood cells, followed by its phosphorylation, affecting the immune system.
Okada and colleagues in Japan compared the levels of AKT phosphorylation in four APDS patients and in a small group of people with other types of antibody-deficient primary immunodeficiency. They found that people with APDS and an APDS-like syndrome all showed enhanced AKT phosphorylation in fresh B cells (taken from their peripheral blood) compared to healthy people and to people with other antibody-deficient primary immune deficiencies.
Rapid and accurate diagnosis of people with APDS can lead to the prescription of more targeted treatments. “This method can diagnose a patient in one day,” says Okada. It can also be used to validate a diagnosis of APDS in people where genetic analyses find unknown mutations in one of the syndrome’s known causative genes.
“Next we plan to investigate why only B cells from the peripheral blood show increased pAKT,” says Okada. “We suspect that increased pAKT is harmful to B cells and we want to understand why.”
The program-affiliated researchers contributing to this research are from the Hiroshima University Graduate School of Biomedical and Health Sciences, Japan.
- Asano, T., Okada, S., Tsumura, M., Yeh, T-W., Mitsui-Sekinaka, K. et al. Enhanced AKT phosphorylation of circulating B cells in patients with activated PI3Kδ syndrome. Frontiers in Immunology 9, 568 (2018).| Article