Lymphocyte Vacuolization Might Be Used to Measure Batten Severity

The number of fluid-containing cellular compartments called vacuoles within immune cells could help to predict the severity of Batten disease, a new study suggests.

The study, “Quantifying lymphocyte vacuolization serves as a measure of CLN3 disease severity,” was published in JIMD Reports.

Vacuoles are compartments within cells that are filled with fluid, often looking like bubbles under a microscope. The process of forming vacuoles is called vacuolization. Lymphocytes — a class of immune cell important for fighting infection — undergo vacuolization in response to infection.

Abnormally high lymphocyte vacuolization has been observed in people with Batten disease. However, it hasn’t been clear whether there is any diagnostic or prognostic relevance to this observation.

In the new study, researchers collected 67 blood samples from 19 people with CLN3 disease, also known as juvenile Batten disease. Those included spanned a wide range of disease severity. For comparison, samples also were collected from individuals without Batten disease (controls). Lymphocyte vacuolization was analyzed by a battery of different tests.

“We hypothesized that quantifying lymphocyte vacuolization would provide an objective diagnostic marker that simultaneously allows to assess disease severity,” the researchers wrote.

The degree of vacuolization was not significantly associated with age or follow-up time. That’s why, according to the researchers, measuring lymphocyte vacuolization likely isn’t a good way to assess disease progression.

In general, more vacuolization — both in terms of more lymphocytes with vacuoles, and the number of vacuoles within individual cells — was observed in samples from people with Batten disease, compared to those from controls.

Increased vacuolization also was associated with more severe forms of the disease. For instance, there was less vacuolization seen in individuals with a more delayed disease onset. Furthermore, individuals with more severe (larger) mutations in the CLN3 gene, which usually are associated with more severe disease, tended to have more vacuolization.

The researchers also measured levels of the protein LAMP-1 in cells; this protein is associated with the formation of vacuoles. LAMP-1 levels were higher in lymphocytes from people with Batten disease and also related metabolic conditions (e.g., sialidosis). However, the increase in LAMP-1 was seen in cells that had a lot of vacuolization, and also in cells with relatively little.

“Together, these results indicate that LAMP‐1 expression may be used to aid diagnosis of diseases associated with lymphocyte vacuolization and furthermore implies that its distribution within lymphocyte subsets may represent a disease specific ‘signature,'” the researchers wrote.

Collectively, these findings indicate that lymphocyte vacuolization is increased in CLN3 disease and is associated with more severe disease, suggesting that measuring lymphocyte vacuolization could be of diagnostic or prognostic value for Batten disease.

Researchers noted that this may be particularly useful for individuals who have a variant of uncertain significance — that is, a mutation in CLN3 that has not been definitively linked to Batten disease. Measuring lymphocyte vacuolization also may be a useful metric in clinical trials.