Predominantly antibody deficiencies are one of the most complex disorders among Inborn Errors of Immunity, with common variable immunodeficiency (CVID), a highly heterogenous and with largely unknown etiology, being the most complex PAD disorder. This study evaluated the peripheral blood lymphocytes population and B cell subsets, which have proven to be useful in the classification of PAD patients and as a first approximation to the probable physiopathology mechanism of the disorder[9, 13].
Analysis of blood lymphocytes showed an increasement in lymphocytes absolute counts, T cells and particularly CD8+ T cells in CVID participants, which was reflected in the CD4:CD8 ratio below the normal value in PAD participants (Table 2). CVID patients also had lower median of NK cells and increased double negative (CD4-CD8-) T cells when compared to health donors. Total memory, switched and unswitched memory B cells were the subsets most frequently altered in PAD. We also found an alteration in the correlation between B cell subsets (figure 4), suggesting that alterations in these subpopulations also affect how they correlate with each other.
Experimental Data has revealed disturbance in the T cells compartment in CVID patients, however, data is still limited. Reduction in CD4+ T cells and expansion of CD8+ T cells with a senescence phenotype has been found that alter the CD4:CD8 ratio but without the common presentation of T cell alterations such as viral and fungal opportunistic infections[18, 19]. Similar to the reported, CVID participants in this study showed alterations in T cell compartment, however CD4+ T cells absolute counts were normal but CD8+ T cells were significantly increased, disturbing the CD4:CD8 ratio, increased double negative T cells and NK cells. SIgAD patients do not showed any significance alteration in this compartment and SIgMD participants had increased CD4+ T cells, suggesting that CVID, but also non-CVID PAD patients had alterations in T and NK cell compartment, however, a more precise immunophenotyping is needed to identified T cell and NK cell subsets alterations.
Alteration in B cell subsets has been recognized to be present in PAD patients, although CVID patients are the more widely studied[9, 14, 20, 21]. It was found that the most frequently altered B cell subsets in PAD participants were the B memory compartment, especially Switched memory B cells, and plasmablasts, even in non-CVID PAD patients, when compared to the median of healthy donors (figure 3) and to the age range-matched healthy donors (Table 2), indicating that this subsets are the most frequently altered as previously reported in Colombian CVID patients, however, no participant showed alterations neither in the frequency of Naïve CD5+ (also known as pre-naïve B cells) that had been associated with autoimmunity nor the naïve CD5- B cells, as reported in a high percentage in the Colombian CVID patients mentioned above, and 4/9 patients showed less than 1% B cells, suggesting a different alterations in B cell subsets between these two geographical areas of Colombia, although the comparison has to be taken with precautious as different markers and gating strategy were used for the identification of B cell subsets. Furthermore, one CVD patient had no reduction in switched or unswitched memory B cells, which implies a different alteration pattern.
Accordingly, classification of EUROclass of this patient did not classified it in a group associated with non-infectious complications and the classification of Driessen et al classified it in the pattern of Post germinal center defect, although most of CVID participants were classified as pattern 1 (B-cell production and germinal center defect) and pattern 3 (B-cell activation and proliferation defect). SIgAD participants showed similar alterations to CVID individuals, implying a possible similar pathological mechanism, two out of the four participants had B-cell activation and proliferation defect. On the other hand, SIgMD showed increased numbers of switched memory B cells and plasmablasts, implying a possible skewness toward isotype-switched phenotypes, at least in the two patients analyzed. This finding highly the importance of B cell subsets analysis in PAD patients, as they are a heterogeneous population.
PAD patients, as showed here, also has alterations in B cell subsets correlation, which further implies a complex alteration in these disorders. The most striking being the loss of correlation between switched memory B cells with all other cells and a positive correlation between transitional B cells and CD21low B cells, which suggest that the more numbers of transitional B cells, the more numbers of CD21low B cells and a negative correlation between switched memory B cells and CD21 low B cells, implying that the more profound the alteration in this memory B cells, the higher the frequency of CD21low B cells.
Euroclass and Driesse et al classifications are important because can potentially modified how the patients are monitored longitudinally in time, with smB-Trnorm and smB-21norm being the patients with most probability to develop any non-infectious complication such as granulomas, autoimmunity and lymphoproliferation but also are important as a started point to further studies about the precise determination of the molecular altered mechanism/s in these patients, which would provide information for the understanding of the disease and the development of better treatments.
Finally, it was also found disturbance in B cell subsets in the non-PAD participants with bronchiectasis, recurrent pneumonia or both conditions as well as reduction in NK cells in recurrent pneumonia group. A previous study reported that non-PAD bronchiectasis patients have quantitative alterations in B cells, CD4+ T cells, IgG3 and neutrophil respiratory burst. We showed here that patients with this pulmonary disease also have alteration in B cell subsets, although it is not possible to determine whether this disturbance contribute to the bronchiectasis development or the bronchiectasis itself lead to the B cell compartment alterations. Adults with recurrent pneumonia are less studied, but analysis of the six patients revealed alterations in the B cell subpopulations as well. Further studies are required to precisely determine whether the alterations in immune function of patients with these pulmonary diseases is significantly contributing to the clinical phenotype.
In conclusion, PAD participants showed alterations in lymphocytes populations and B cell subsets, as well as disturbance in the correlation of these B cells subpopulations, especially in switched memory B cells. Furthermore, classification of these patients revealed different probable pathophysiological mechanism of their disease, suggesting a heterogenous population of PAD patients attended in southwestern Colombia. However, the numbers of PAD participants included in this study is not optimal for statistical analysis due to the high complexity and heterogeneity of PAD disorders, therefore, studies with more patients are needed. But more importantly, this study not only highly the importance of B cell subsets analysis in PAD patients, which are currently understudied in Colombia, but also in non-PAD patients with bronchiectasis and recurrent pneumonia.