Transmembrane tumor necrosis factor alpha is required for enteropathy and is sufficient to promote parasite expulsion in gastrointestinal helminth infection.

To study the specific role of transmembrane tumor necrosis factor (tmTNF) in protective and pathological responses against the gastrointestinal helminth Trichinella spiralis, we compared the immune responses of TNF-alpha/lymphotoxin alpha (LTalpha)(-/-) mice expressing noncleavable transgenic tmTNF to those of TNF-alpha/LTalpha(-/-) and wild-type mice. The susceptibility of TNF-alpha/LTalpha(-/-) mice to T. spiralis infection was associated with impaired induction of a protective Th2 response and the lack of mucosal mastocytosis. Although tmTNF-expressing transgenic (tmTNF-tg) mice also had a reduced Th2 response, the mast cell response was greater than that observed in TNF-alpha/LTalpha(-/-) mice and was sufficient to induce the expulsion of the parasite. T. spiralis infection of tmTNF-tg mice resulted in significant intestinal pathology characterized by villus atrophy and crypt hyperplasia comparable to that induced following the infection of wild-type mice, while pathology in TNF-alpha/LTalpha(-/-) mice was significantly reduced. Our data thus indicate a role for tmTNF in host defense against gastrointestinal helminths and in the accompanying enteropathy. Furthermore, they also demonstrate that TNF-alpha is required for the induction of Th2 immune responses related to infection with gastrointestinal helminth parasites.

Neutrophil swarming and extracellular trap formation play a significant role in Alum adjuvant activity.

There are over 6 billion vaccine doses administered each year, most containing aluminium-based adjuvants, yet we still do not have a complete understanding of their mechanisms of action. Recent evidence has identified host DNA and downstream sensing as playing a significant role in aluminium adjuvant (aluminium hydroxide) activity. However, the cellular source of this DNA, how it is sensed by the immune system and the consequences of this for vaccination remains unclear. Here we show that the very early injection site reaction is characterised by inflammatory chemokine production and neutrophil recruitment. Intravital imaging demonstrates that the Alum injection site is a focus of neutrophil swarms and extracellular DNA strands. These strands were confirmed as neutrophil extracellular traps due to their sensitivity to DNAse and absence in mice deficient in peptidylarginine deiminase 4. Further studies in PAD4-/- mice confirmed a significant role for neutrophil extracellular trap formation in the adjuvant activity of Alum. By revealing neutrophils recruited to the site of Alum injection as a source of the DNA that is detected by the immune system this study provides the missing link between Alum injection and the activation of DNA sensors that enhance adjuvant activity, elucidating a key mechanism of action for this important vaccine component.

Contrasting effects of acute and chronic gastro-intestinal helminth infections on a heterologous immune response in a transgenic adoptive transfer model.

We have previously found that co-immunisation with ovalbumin (OVA) and the body fluid of the helminth Ascaris suum inhibited an OVA-specific delayed type hypersensitivity (DTH) response by reducing OVA-specific CD4+ T lymphocyte proliferation via an IL-4 independent mechanism. In the present study, we determined whether parasite infections themselves could induce similar changes to peripheral immunisation by examining the modulation of OVA-specific immune responses during acute and chronic helminth infections. Surprisingly, an acute infection with Trichinella spiralis, but not a chronic infection with Heligmosomoides polygyrus, inhibited the OVA-specific DTH reaction. Correspondingly, the T helper 1 (Th1) OVA-specific response was decreased in mice infected with T. spiralis, but not with H. polygyrus. Inhibition of the Th1 response may be a result of a shift in the Th1/Th2 balance as although both H. polygyrus and T. spiralis infected mice induced a Th2 OVA-specific response, that exhibited by T. spiralis was more potent. Furthermore, although IL-10 secretion upon OVA restimulation was similarly increased by both infections, production of this immunoregulatory cytokine may play a role in the suppression of immune responses observed with T. spiralis infection depending on the context of its release. Interestingly, analysis of the OVA-specific T lymphocyte division by carboxyfluorescein diacetate succinimidyl ester (CFSE) staining revealed that gastro-intestinal infection with the acute helminth T. spiralis, but not with chronic H. polygyrus, inhibited the systemic immune response by significantly inhibiting the antigen-specific T cell proliferation during the primary response, a mechanism similar to that observed when A. suum parasite extracts were directly mixed with the OVA during immunisation in our previous studies.

Mast cell production of IL-4 and TNF may be required for protective and pathological responses in gastrointestinal helminth infection.

Expulsion of the gastrointestinal nematode Trichinella spiralis is associated with Th2 responses and intestinal inflammation, which correlate with a marked mast cell (MC) response. To address the role of MC-derived cytokines in the induction of protective responses, WBB6F1-KitW/KitW-v (W/W(v)) mice were reconstituted with wild-type, tumor necrosis factor (TNF)-alpha(-/-), or interleukin (IL)-4(-/-) bone marrow (BM) prior to infection with T. spiralis. W/W(v) mice reconstituted with TNF-alpha(-/-) or IL-4(-/-) BM expelled the parasite less efficiently and showed diminished enteropathy, whereas protective responses were normal in W/W(v) mice reconstituted with wild-type BM and were accompanied by intestinal pathology. MC responses were reduced in W/W(v) mice reconstituted with IL-4(-/-) BM and to a lesser extent when reconstituted with TNF-alpha(-/-). These results suggest that MC-derived IL-4 and TNF may regulate the induction of protective Th2 responses and intestinal inflammation associated with the expulsion of T. spiralis. Significantly, these studies suggest a role for MC-derived cytokines as autocrine growth factors.

The role of IL-4, IL-13 and IL-4Ralpha in the development of protective and pathological responses to Trichinella spiralis.

T helper type 2 (Th2) responses have been shown to be important in protective responses to gastrointestinal (GI) helminth infections and in the development of the intestinal pathology accompanying expulsion of the parasite. Different inbred mouse strains have been shown to develop different cytokine profiles following infection with GI helminths with increased resistance observed in those strains where Th2 cytokines predominate. The aim of this study was to determine the role of IL-4, IL-13 and IL-4Ralpha and the impact of host background on the development of the protective and pathological responses induced by infection with the gastrointestinal helminth Trichinella spiralis. IL-4, IL-13 and IL-4Ralpha were required for the generation of Th2 responses to T. spiralis; however, the role these responses play in the development of protection and enteropathy was less clear. IL-4Ralpha-deficiency mice resulted in substantially reduced parasite expulsion, intestinal pathology and Th2 responses. Similarly, lack of IL-13 resulted in inhibited expulsion and the development of enteropathy. Although Th2 responses were reduced in BALB/c IL-4-/- mice, neither expulsion nor enteropathy were different from wild-type mice. In contrast, C57BL/6 IL-4-/- exhibited delayed expulsion and reduced pathology, suggesting that host genetics are important in the function of individual cytokines. Thus, differences in background genotype may be an important component in the development host protection and the development of intestinal pathology accompanying the loss of GI helminths.