The activation of BAFF/APRIL system in spleen and lymph nodes of Plasmodium falciparum infected patients

Abstract

Previous studies have reported activation of the B cell-activating factor (BAFF)/a proliferation-inducing ligand (APRIL) system in T independent immunity against malaria infection. Plasmodium falciparum (P. falciparum) infected animal model is not feasible. Therefore, little is known about the occurrence of BAFF/APRIL system and changes in falciparum lymphoid tissues. This study aimed to investigate the expression of BAFF/APRIL system components in lymphoid tissues from P. falciparum infected patients. Spleen and lymph node samples from 14 patients were collected at autopsy. Normal spleens and bacterially infected tonsils served as controls. The protein and/or mRNA expression of BAFF/APRIL and their cognate receptors, BAFF-R, TACI and BCMA, were determined by immunohistochemistry and RT-qPCR, respectively. The spleens of the patients exhibited significantly higher BAFF-R protein expression than normal spleens. Although without appropriate control, BCMA protein was markedly observed only in the lymph nodes. BAFF and BCMA mRNA levels were also significantly elevated in the spleen tissues of the patients compared with normal spleens. The overall BAFF-R protein levels in the lymphoid tissues of the patients correlated positively with parasitaemia. These findings are the first to confirm that BAFF/APRIL system activation in lymphoid tissues and is positively correlated with the parasitaemia levels in falciparum malaria.

Figure 1

Histopathological staining of human lymphoid tissue sections. H&E staining of sections of normal spleen, spleen and lymph node from a patient with falciparum malaria, and bacterially infected tonsil at magnification ×40 (a) and ×1000 (b).

Figure 2

Expression of BAFF/APRIL and the cognate receptors in human lymphoid tissue sections. (a) Immunohistochemical staining of BAFF-R and BCMA in sections of normal spleen, spleen and lymph node from a patient with falciparum malaria, and bacterially infected tonsil at magnification ×1000. Negative = staining without primary antibody; single staining for BAFF-R or BCMA is brown; double staining for BAFF-R is brown in B cells (IgD+) is red. (b,c) Semi-quantification of immunohistochemical staining of BAFF-R and BCMA; (b) Representative images of spleen tissue sections from a patient with falciparum malaria stained with immunoperoxidase and DAB for BAFF-R showing intensity scores ranging from negative (−) to strongly positive (+4); (c) Heat maps showing intensity of total score immunoreactivity (the percentage of B cells with positive immunoreactivity × the intensity score) for BAFF-R (left panel) and BCMA (right panel); (d) Box and whisker plots showing total scores (percentage of B cells with positive staining × intensity score) for BAFF-R (left panel) and BCMA (right panel) expression in the indicated lymphoid tissue sections. Horizontal bar, box edges, and whiskers represent the median, the first/third quartiles, and the min/max values, respectively; (e) Correlations between parasitaemia and total staining scores for BAFF-R in spleen (left panel) or in both lymphoid tissues (lower panel), or BCMA in spleen of the malaria patients (right panel) using Spearman’s rank correlation test with a significance value of p < 0.05. (f) and (g) RT-qPCR analysis of BAFF, APRIL, BAFF-R, TACI, and BCMA mRNA levels in (f) spleens (fold change), and (g) lymph nodes (ACTB mRNA ratio) from patients with falciparum malaria or bacterially infected tonsil (positive control). Data were normalized to ACTB (β-actin) mRNA in the same sample. The results in the spleen of falciparum malaria patients are presented as the fold change in expression relative to the levels in the normal spleen samples using the 2^−(ΔΔCt) method. The results for the lymph node tissues of the patients and tonsillitis were represented as ACTB mRNA ratio.