Nematospiroides dubius and Nippostrongylus brasiliensis: delayed type hypersensitivity responses to ovalbumin in the infected mouse

Worms as therapeutic agents for allergy and asthma: understanding why benefits in animal studies have not translated into clinical success

Helminth infections are associated with decreased rates of autoimmunity and allergy, and several clinical studies have demonstrated that intentional infection with helminths can reduce symptoms of autoimmune diseases. In contrast, though numerous animal studies have demonstrated that helminth infections ameliorate allergic diseases, clinical trials in humans have not shown benefit. In this article, we review in detail the 2 human studies that have prospectively tested whether helminth infections protect against allergy. We next review the research designs and results obtained from animal studies, and compare these to the human trials. We then postulate possible reasons for the lack of efficacy observed in clinical trials to date and discuss potential future areas of research in this field.

Heligmosomoides polygyrus promotes regulatory T-cell cytokine production in the murine normal distal intestine

Helminths down-regulate inflammation and may prevent development of several autoimmune illnesses, such as inflammatory bowel disease. We determined if exposure to the duodenal helminth Heligmosomoides polygyrus establishes cytokine pathways in the distal intestine that may protect from intestinal inflammation. Mice received 200 H. polygyrus larvae and were studied 2 weeks later. Lamina propria mononuclear cells (LPMC) were isolated from the terminal ileum for analysis and in vitro experiments. Mice with H. polygyrus were resistant to trinitrobenzenesulfonic acid (TNBS)-induced colitis, a Th1 cytokine-dependent inflammation. Heligmosomoides polygyrus did not change the normal microscopic appearance of the terminal ileum and colon and minimally affected LPMC composition. However, colonization altered LPMC cytokine profiles, blocking gamma interferon (IFN-gamma) and interleukin 12 (IL-12) p40 release but promoting IL-4, IL-5, IL-13, and IL-10 secretion. IL-10 blockade in vitro with anti-IL-10 receptor (IL-10R) monoclonal antibody restored LPMC IFN-gamma and IL-12 p40 secretion. IL-10 blockade in vivo worsened TNBS colitis in H. polygyrus-colonized mice. Lamina propria CD4(+) T cells isolated from colonized mice inhibited IFN-gamma production by splenic T cells from worm-free mice. This inhibition did not require cell contact and was dependent on IL-10. Heligmosomoides polygyrus colonization inhibits Th1 and promotes Th2 and regulatory cytokine production in distant intestinal regions without changing histology or LPMC composition. IL-10 is particularly important for limiting the Th1 response. The T-cell origin of these cytokines demonstrates mucosal regulatory T-cell induction.

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.

Depression of humoral responses by murine cytomegalovirus infection

The ability of mice infected with murine cytomegalovirus (MCMV) to respond to unrelated antigens in vivo was studied in genetically sensitive BALB/c and genetically resistant CBA mice. Suppressed humoral responses were observed following intraperitoneal or intravenous antigen challenge a few days after infection. IgG production was depressed more frequently than IgM. The suppression was correlated with splenic atrophy and hyporesponsiveness of the residual spleen cells in vitro. The peritoneal macrophage response to intraperitoneal adjuvant challenge was also modified by the infection. Subcutaneous antigenic challenge elicited normal or elevated humoral and delayed-type hypersensitivity responses, during which peripheral lymph nodes were consistently expanded. Antigen administered intraperitoneally without adjuvant on the day of infection also evoked elevated humoral responses. This correlates with the host's ability to respond to MCMV itself, possibly via primed cells seeded to the lymph nodes before the spleen was damaged by the infection.

Altered immune response (humoral and delayed-type hypersensitivity reactions) to sheep red blood cells in the course of experimental filarial infections (Litomosoides carinii, Brugia malayi, Acanthocheilonema viteae) of Mastomys natalensis

Litomosoides carinii-, Acanthocheilonema viteae- or Brugia malayi-infected Mastomys natalensis were sensitised against sheep red blood cells (SRBC) on various occasions after infection to determine the effect of filarial infections on the immune response to a non-filarial antigen. The phagocytic activity of the reticuloendothelial system (RES) was controlled in vivo by the elimination of 51Cr-labelled SRBC. Antibody titres against SRBC (agglutinating and lytic antibodies) were similar to those of uninfected controls in L. carinii- or B. malayi-infected Mastomys sensitised during prepatency or early patency up to 90 days post infection (p.i.) but were reduced in animals sensitised during patency. A significant inverse correlation existed between anti-SRBC antibody titres and microfilaraemia levels. In contrast, A. viteae-infected Mastomys showed reduced humoral anti-SRBC responses at the end of prepatency, whereas the response tended towards normal with increasing parasitaemia. Delayed-type hypersensitivity (DTH) against SRBC was measured as footpad swelling after sensitisation by the s.c. or i.v. route and intraplantar challenge. DTH reactions were reduced during prepatency in all infections after s.c. sensitisation. During patency, 24-h reactions were similar to those of age-matched controls but the swelling persisted 24 or 48 h longer than in the latter. In A. viteae infections, even enhanced 24-h reactions were found during patency. Histological investigations did not reveal differences in the type of cell infiltrations between infected and control animals. After i.v. sensitisation with SRBC, L. carinii- and A. viteae-infected animals showed weaker DTH reactions than the controls, independent of the period after infection. In the case of B. malayi infections, DTH reactions were similar to those of controls during early prepatency, whereas reduced DTH responses were observed later than 50 days p.i. As shown in L. carinii-infected animals, depressed DTH reactions after i.v. sensitisation did not depend on an altered expression phase but rather on an altered regulation during the inductive phase of the response: increases in the sensitising SRBC doses that caused decreasing DTH reactions in uninfected animals led to enhanced reactions in infected animals. Phagocytosis of i.v. injected 51Cr-labelled SRBC was enhanced during prepatency in L. carinii infection and during patency in all infections.