Immune cell reduction still seen 10 months after COVID-19 infection

Key takeaways:

• Even 10 months after infection, patients showed changes in T-cell subsets and other immune cell reductions.
• The immune cell changes point to long-term COVID-19 effects.

Patients infected with SARS-CoV-2 showed signs of reduced immune cells and a change in growth factor patterns in their blood 10 months after infection, according to a study published in Allergy.

Patients showed a reduction of T cells and B cells after first contracting COVID-19, Bernhard Kratzer, PhD, post-doctoral researcher, center for pathophysiology, infectiology and immunology, Institute of Immunology, Medical University of Vienna, and colleagues wrote. A reduction in neutrophils, monocytes and natural killer (NK) cells were also found, showing that a single SARS-CoV-2 infection can have long-lasting effects.

Methods, background

Kratzer and colleagues conducted a longitudinal study between May and August 2020 when the Wuhan-Hu-1 was the only circulating virus strain. The study included 132 patients (mean age, 49.7 years; age range, 16-78 years; 46.2% female) with an real-time PCR-confirmed COVID-19 diagnosis and/or an antibody test confirmed diagnosis analyzed at 10 weeks and 10 months after infection. Ultimately, 106 patients were analyzed.

The control group consisted of 98 noninfected subjects (mean age, 50.1 years; age range, 14-77 years; 55.1% female).

Blood was drawn from each study participant and was either EDTA-anticoagulated, heparin-anticoagulated or silicon dioxide coagulated. Analyzed patients were divided based on their SARS-CoV-2 specific antibody decrease pattern.

Group 1 had a low to moderate decrease of nucleocapsid (NC)-specific antibody levels of 50% or less with variable decreases of spike (S)-specific antibody levels. Group 2 had a high decrease in NC-specific antibody levels of more than 50% and a low decrease in S-specific antibody levels of 40% or less. Group 3 had both high decreases of NC specific antibody levels of greater than 50%-and S specific antibody levels of greater than 40%.

COVID-19 vaccines were not yet available when the study was conducted, and no infected individuals reported symptoms between the two visits at 10 weeks and 10 months. Disease course in the 132 infected patients was severe or critical (2.3%), moderate (8.3%) and mild (87.1%), whereas 2.3% were asymptomatic.

Among the 106 analyzed patients, 87 patients (65.9%) reported comorbidities with 68 (64.2%) in the antibody decrease group.

The most common comorbidities were allergic diseases in the infected group (36.4%) and the control group (43.9%). Additional comorbidities shown in more than 10% of study subjects included cardiovascular diseases, metabolic diseases and chronic lung diseases.

Regular medication intake to treat comorbidities were reported by 60 (45.5%) participants in the infected group and 48 (49%) in the control group.

Results

Researchers found that serum IgG antibody levels specific for S, receptor-binding domain (RBD) and NC declined a few months after a patient’s first SARS-CoV-2 infection.

Among the 106 infected participants, the anti-S protein serum IgG levels significantly decreased from 10 weeks to 10 months (P < .0001). Three participants (2.8%) had levels below the cutoff value at 10 weeks, which increased to 19 patients (17.9%) at 10 months, (P = .0005). There was also significant decrease of anti-RBD IgG antibody levels from 10 weeks to 10 months (P < .0001).

Also among the infected patients, 26 patients (24.5%) had anti-RBD serum IgG levels below the cutoff value at 10 weeks, with this number increasing at 10 months to 86 patients (81.1%) (P < .0001). At both 10 weeks and 10 months, none of the 106 patients were NC negative, showing that NC-specific IgG is a more reliable marker for confirming previous COVID-19 infection.

Among the 106 patients that at 10 weeks saw a decrease in S-RBD and NC antibodies, 52 (49.1%) showed protective neutralizing antibody levels above the cutoff for 25% of inhibition. This number shrank to 10 patients (9.4%) at 10 months (P < .0001). The mean percent inhibitions fell from 25.8% at 10 weeks to 10.8% at 10 months. An inhibition score of more than 50% was seen in 20 patients at 10 weeks and one patient at 10 months.

The mean cutoff index significantly decreased for anti-NC antibody between 10 weeks and 10 months (P < .0001). Researchers noted the percentage decrease in NC antibody levels had a significant correlation with the decrease in S antibody levels (P = .0003).

There was a significant difference in the mean age in antibody decrease groups 1 and 3 by 10.3 years (P = .0072). S antibody levels were higher in group 1 than in group 3 (P = .0089). There were similar significant drops in neutralizing antibody levels in group 1 (P =.0106) and group 3 (P < .0001). Only six patients (25%) in group 2 had an initial blocking activity of more than 25% which did not occur in any patients at the 10-month mark.

Researchers also examined the impact of COVID-19 on blood leukocyte populations at 10 months after infection. When compared with 10 weeks after infection, the infected group had significantly lower total leukocyte counts at 10 months (P < .0001).

Specifically, neutrophil counts declined at 10 months (P <.001). Monocyte and lymphocyte counts also were significantly lower in the infected group at 10 months compared with 10 weeks (P < .0001).

The CD3⁺CD4⁺ helper and CD3⁺CD8⁺ cytotoxic T-cell subsets both were affected by the reduction in T cells at 10 months. The observed signs of T-cell activation at 10 weeks affecting both the CD3⁺CD4⁺ and CD3⁺CD8⁺ T-cell subsets and seen by neo-expression of HLA-DR and CD38 mostly disappeared by 10 months.

Also at the 10-month mark, the 10 patients that required hospitalization due to severe COVID-19 illness still had elevated numbers of HLA-DR⁺ and HLA-DR⁺T cells.

The NK cell numbers in infected patients were also significantly lower at 10 months (P < .0001) compared with 10 weeks. This drop was primarily seen in group 2 (P = .0021) and group 3 (P = .0015).

B cell decrease was observed in the entire study group. A significant drop was seen in group 2 (P = .0338) and in group 3 (P < .0001).

Recent thymic emigrants (RTEs), which were the most naïve T cells (CD3⁺CD45RA⁺CD62L⁺CD31⁺) were almost halved at 10 months compared with 10 weeks (P < .0001).

This affected the helper T cell subset (CD4⁺CD45RA⁺CD62L⁺CD31⁺; reduction, 52.1%; P < .0001) more than the cytotoxic T cell subset (CD8⁺CD45RA⁺CD62L⁺CD31⁺; reduction, 34.1%; P < .0001).

Researchers also noted that younger vs. older patients had significantly more circulating RTE numbers (P < .0001). The COVID-19 drop in RTE numbers at 10 months was seen across all age groups. In 93 of 104 (CD3⁺CD4⁺, 89.4%) and in 83 of 104 (CD3⁺CD8⁺, 79.8%) of the infected patients, the peripheral blood RTE subsets were significantly more reduced at 10 months than at 10 weeks.

At 10 months there was also an increase of absolute numbers of CD3⁺CD45RO⁺CCR7⁺ central memory CD4⁺ and CD8⁺ T cell subsets, with an increase of 22% in CD4⁺ (P = .0041) and an increase of 160% in CD8⁺ (P = .0001).

When compared with 10 weeks, at 10 months, the CD4⁺CD45RO⁺CCR7⁺ central memory T-cell subset increased for 55 of 100 patients (55%), and the CD8⁺CD45RO⁺CCR7⁺ T-cell memory cell subset increased for 67 of 98 patients (68.4%).

During the 10-month observational period, high levels of CD3⁺CD4⁺CD45RA⁺CD127⁺ cells persisted (P < .0001 and P < .0001 vs. noninfected control subjects, respectively).

In regard to the significant loss of B cells and B-cell subsets between the 10 week and 10 month period after the first COVID-19 infection, there was a significant reduction of overall circulating CD19⁺CD21⁺CD27⁺ memory B cells (P = .0027). This was due to a decrease of non-class switched CD19⁺IgD⁺CD27 memory B cells (P = .0034).

The subset of CD5⁺ B1-like marginal zone B cells also was significantly reduced at 10 months in absolute (P < .0001). All three groups experienced a drop in CD5+ cells (group 1, P = .0462; group 2 and group 3, P < .0001).

Researchers also examined the serum Th1, Th2, Th17 and inflammatory cytokine levels in the study groups. Infected patients had higher levels of IL-1B, IL-8 and IL-12 10 weeks after infection compared with the control group, but these increases had resolved by the 10-month mark.

Elevated IL-4 and IL-10 serum levels (7.3-fold, P < .001 and 1.7-fold, P = .03, respectively) showed Th2-dominated serum cytokine patterns at 10 months compared with 10 weeks after infection.

There were also significantly lowered IFN-gamma and IL-21 levels compared with the control group (P < .0001 for both). The IFN-gamma and IL-4 ratios of COVID-19 infected patients changed from 6.82 to 0.21 between 10 weeks and 10 months compared with the control group (P < .0001).