A new study of immunoglobulin levels in adult patients with systemic lupus erythematosus (SLE) has found that acquired low levels of IgA are associated with a higher risk of infection.
Dr. Karen Costenbader
To the knowledge of first author Ibrahim Almaghlouth, MD, of the division of rheumatology at the University of Toronto, and colleagues, “this is the first dedicated study to examine the relationship between acquired low immunoglobulins and infection risk in adult patients with SLE.” But as to whether there may be a “protective role for immunoglobulins and the potential effect of immunoglobulin replacement in a setting of recurrent or severe infection among SLE patients requires further study.”
To determine if the risk of infection was tied to acquired low immunoglobulin levels, the researchers launched a retrospective analysis of data from a prospective cohort study of adult SLE patients from a Toronto lupus cohort that was established in 1970. The study was published in Rheumatology.
A total of 448 patients with at least two low immunoglobulin tests were matched with 656 SLE patients with no low immunoglobulins according to enrollment decade. The average age of the low-immunoglobulin group was 41.8 years, compared with 39.3 years in the control group. Average disease duration was 11.2 years in the low-immunoglobulin group and 7.6 years in the control group.
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Of the patients in the low-immunoglobulin group, 221 had consecutive low tests and 227 had nonconsecutive low tests. Overall, 98 of those patients had low IgG, 251 patients had low IgM, and 51 patients had low IgA. Only 48 patients had overlapping low levels, including 5 with all three.
Average levels among the low-immunoglobulin group at baseline were 11.5 (standard deviation, 6.1) g/L of IgG, 0.8 (1.1) g/L of IgM, and 2.4 (1.6) g/L of IgA, while average levels among the control group were 16.3 (6.4) g/L of IgG, 1.8 (1.2) g/L of IgM, and 3.2 (1.5) g/L of IgA. In the primary analysis, after adjustment using propensity scoring, there were 97 infections: 47 in the low-immunoglobulin group and 50 in the control group. The most common types were respiratory and urinary tract infections, and the rate of infection was higher in patients with low IgA. The IgA level associated with risk of infection was less than 0.75 g/L.
After Cox regression analysis, the only variable that significantly increased infection risk was a low IgA level (hazard ratio, 3.19; 95% confidence interval, 1.17-8.71), not a low IgG level (HR, 1.87; 95% CI, 0.77-4.54) or low IgM level (HR, 0.63; 95% CI, 0.34-1.17). In regard to recovery among the low-immunoglobulin group, 11 patients (2.5%) recovered from low immunoglobulins within in the first year, followed by 36 (8.2%) in the second year, 44 (10.1%) in the third year, and 80 (18.4%) in the fourth year. All told, 60% (263) of patients with acquired hypogammaglobulinemia recovered over a 4-year period.
Is there clinical relevance to low IgA?
“I don’t see us using this clinically immediately,” Karen Costenbader, MD, a rheumatologist at Brigham and Women’s Hospital and professor of medicine at Harvard Medical School, both in Boston, said in an interview. “We do test immunoglobulins often, especially in patients who’ve had biologic therapy. Will we start thinking about their IgA levels? It’s not clear, and the researchers leave it up in the air as to what this means, beyond them being at high risk.”
That said, she added, “IgA levels are interesting, especially in a time of COVID, because they’re associated with mucosal immunity. Is this subset of patients going to be at particularly high risk for the coronavirus?”
She also noted that, though immunoglobulin replacement has been helpful in her patients, it’s an expensive therapy to recommend for low IgA levels without knowing exactly what is causing these deficiencies. “My question is, would it be useful to follow these levels in lupus patients, even we don’t know what to do about them?” she asked. “We know there are a lot of risk factors for infections, so is the IgA going to be useful above and beyond that, and then what can we do about it?”
The authors acknowledged their study’s potential limitations, including low infection rates and yearly measurements of immunoglobulin levels, which could’ve led to misclassifying a lab error as true low immunoglobulin. They also highlighted its strengths, including using various methods to reduce selection and confounding bias while also reporting consistent results after examining multiple definitions of low immunoglobulins and outcomes.
The study received no specific funding, and the authors reported no potential conflicts of interest.
SOURCE: Almaghlouth I et al. Rheumatology. 2020 Oct 2. doi: 10.1093/rheumatology/keaa641.