TNF-α Contributes to Lymphoid Tissue Disorganization and Germinal Center B Cell Suppression during Intracellular Bacterial Infection

Abstract

Bacterial, parasitic, and viral infections are well-known causes of lymphoid tissue disorganization, although the factors, both host and/or pathogen derived, that mediate these changes are largely unknown. Ehrlichia muris infection in mice causes a loss of germinal center (GC) B cells that is accompanied by the generation of extrafollicular T-bet + CD11c + plasmablasts and IgM memory B cells. We addressed a possible role for TNF-a in this process because this cytokine has been shown to regulate GC development. Ablation of TNF-a during infection resulted in an 8-fold expansion of GL7 + CD38 lo CD95 + GC B cells, and a 2.5-and 5-fold expansion of CD138 + plasmablasts and T-bet + memory cells, respectively. These changes were accompanied by a reduction in splenomegaly, more organized T and B cell zones, and an improved response to Ag challenge. CXCL13, the ligand for CXCR5, was detected at 6-fold higher levels following infection but was much reduced following TNF-a ablation, suggesting that CXCL13 dysregulation also contributes to loss of lymphoid tissue organization. T follicular helper cells, which also underwent expansion in infected TNF-a-deficient mice, may also have contributed to the expansion of T-bet + B cells, as the latter are known to require T cell help. Our findings contrast with previously described roles for TNF-a in GCs and reveal how host-pathogen interactions can induce profound changes in cytokine and chemokine production that can alter lymphoid tissue organization, GC B cell development, and extrafollicular T-bet + B cell generation.

Loss of Bcl-6-Expressing T Follicular Helper Cells and Germinal Centers in COVID-19

“…Although, in principle, phenotypically defined CD4 + Bcl-6 + T cells could include both T FH cells and T follicular regulatory cells, we stained cells simultaneously with CD4, CXCR5, FOXP3, and Bcl-6 among other markers and used multispectral imaging to establish that, although there were FOXP3 + T reg cells present, there was no overlap in Bcl-6 and FoxP3 expression in COVID-19 secondary lymphoid organs, indicating that there are very few if any T follicular regulatory cells in COVID-19 ( Figure S3 A). Although there is a developmental role for tumor necrosis factor alpha (TNF-α) in primary lymphoid follicular development ( Pasparakis et al., 1996 ; Körner et al., 1997 ), germinal center loss has been described in the context of cytokine storm in mouse models, reversed by TNF-α blockade ( Ryg-Cornejo et al., 2016 ; Popescu et al., 2019 ), and also linked genetically to an abundance of TNF-α ( Popescu et al., 2019 ). We therefore also examined activated secondary lymphoid tissues from controls and COVID-19 lymph nodes for TNF-α expression.…”

“…These data indicate that the differentiation of activated CD4 + T cells into GC-type Bcl-6 + T FH cells is specifically blocked in COVID-19. Given the information obtained from the above animal models ( Popescu et al., 2019 ; Ryg-Cornejo et al., 2016 ), it is possible that the aberrant and exuberant synthesis of TNF-α at the site of T FH differentiation in COVID-19 lymph nodes may contribute to the lack of germinal centers and the impaired quality and durability of the antibody response to SARS-CoV-2 in this disease.

Figure 3 Loss of Germinal Center Type Bcl-6 + T Follicular Helper Cells in COVID-19 Lymph Nodes and Spleens (A) Representative multi-color immunofluorescence image of CD4 (red), ICOS (green), and DAPI (blue) staining in lymph nodes from early (left) and late (middle) COVID-19 patients and a non-COVID-19 control (right).

…”

“…In a mouse model of severe malaria, germinal center responses were defective, and this was linked to a defect in T follicular helper cell differentiation ( Ryg-Cornejo et al., 2016 ) that could be reversed by TNF-α blockade. Ehrlichia muris infection in mice has also been associated with the loss of germinal centers, and TNF-α blockade restored germinal centers as did the genetic deletion of TNF-α ( Popescu et al., 2019 ). A mouse immunization model that involved prior generation of specific CD4 + T cell memory prior to infection with lymphocytic choriomeningitis virus generated a severe cytokine storm, splenic shrinkage, loss of germinal centers, and bone marrow hypocellularity, suggesting that lymphopenia and lymphoid organ abnormalities may be attributed to immune mechanisms rather than being a direct consequence of viral cytolysis ( Penaloza-MacMaster et al., 2015 ).…”

“…in murine malaria and our studies in COVID-19 suggest that the observed cytokine and chemokine dysregulation may block germinal center type T follicular helper cell differentiation. The contribution of TNF-α to follicular development and germinal center formation ( Pasparakis et al., 1996 ; Körner et al., 1997 ) as well as to the loss of germinal centers is complex and seemingly contradictory ( Ryg-Cornejo et al., 2016 ; Popescu et al., 2019 ). Local cytokine concentrations at the site of T follicular helper cell differentiation likely have important consequences for the germinal center reaction.…”

The effect of hysteroscopic polypectomy on the concentrations of tumour necrosis factor-α in uterine flushings and serum in infertile women

“…The most important physiological functions of cytokines include regulating cell growth and humoral immune response, regulation of hematopoiesis, controlling cell proliferation and differentiation, and wound healing [10][11][12][13]. Cytokines can act locally or systemically [14]. Cellular response to most cytokines is followed by gene expression, which results in the target cell gaining some new functions and can sometimes lead to cell proliferation [15].…”