Characterization and pathological significance of monoclonal DNA-binding antibodies from mice with experimental malaria infection

The influence and therapeutic effect of microbiota in systemic lupus erythematosus

Systemic erythematosus lupus (SLE) is an autoimmune disease involving multiple organs that poses a serious risk to the health and life of patients. A growing number of studies have shown that commensals from different parts of the body and exogenous pathogens are involved in SLE progression, causing barrier disruption and immune dysregulation through multiple mechanisms. However, they sometimes alleviate the symptoms of SLE. Many factors, such as genetic susceptibility, metabolism, impaired barriers, food, and sex hormones, are involved in SLE, and the microbiota drives the development of SLE either by depending on or interacting with these factors. Among these, the crosstalk between genetic susceptibility, metabolism, and microbiota is a hot topic of research and is expected to lay the groundwork for the amelioration of the mechanism, diagnosis, and treatment of SLE. Furthermore, the microbiota has great potential for the treatment of SLE. Ideally, personalised therapeutic approaches should be developed in combination with more specific diagnostic methods. Herein, we provide a comprehensive overview of the role and mechanism of microbiota in lupus of the intestine, oral cavity, skin, and kidney, as well as the therapeutic potential of the microbiota.

The tangled web of autoreactive B cells in malaria immunity and autoimmune disease

Two seminal observations suggest that the African genome contains genes selected by malaria that protect against systemic lupus erythematosus (SLE) in individuals chronically exposed to malaria, but which in the absence of malaria, are risk factors for SLE. First, Brian Greenwood observed that SLE was rare in Africa and that malaria prevented SLE-like disease in susceptible mice. Second, African-Americans, as compared with individuals of European descent, are at higher risk of SLE. Understanding that antibodies play central roles in malaria immunity and SLE, we discuss how autoreactive B cells contribute to malaria immunity but promote SLE pathology in the absence of malaria. Testing this model may provide insights into the regulation of autoreactivity and identify new therapeutic targets for SLE.

Exacerbation of autoimmune neuro-inflammation in mice cured from blood-stage Plasmodium berghei infection

The thymus plays an important role shaping the T cell repertoire in the periphery, partly, through the elimination of inflammatory auto-reactive cells. It has been shown that, during Plasmodium berghei infection, the thymus is rendered atrophic by the premature egress of CD4+CD8+ double-positive (DP) T cells to the periphery. To investigate whether autoimmune diseases are affected after Plasmodium berghei NK65 infection, we immunized C57BL/6 mice, which was previously infected with P. berghei NK65 and treated with chloroquine (CQ), with MOG35-55 peptide and the clinical course of Experimental Autoimmune Encephalomyelitis (EAE) was evaluated. Our results showed that NK65+CQ+EAE mice developed a more severe disease than control EAE mice. The same pattern of disease severity was observed in MOG35-55-immunized mice after adoptive transfer of P. berghei-elicited splenic DP-T cells. The higher frequency of IL-17+- and IFN-γ+-producing DP lymphocytes in the Central Nervous System of these mice suggests that immature lymphocytes contribute to disease worsening. To our knowledge, this is the first study to integrate the possible relationship between malaria and multiple sclerosis through the contribution of the thymus. Notwithstanding, further studies must be conducted to assert the relevance of malaria-induced thymic atrophy in the susceptibility and clinical course of other inflammatory autoimmune diseases.

Biology of autoreactive extrathymic T cells and B-1 cells of the innate immune system

Cumulative evidence has shown that extrathymic T cells can be autoreactive and that B-1 cells may produce autoantibodies. These T and B-1 cells, which form part of the innate immune system, tend to be activated simultaneously when conventional T and B cells are in a suppressive state, for example, when thymic atrophy occurs by stress or involution with aging. In other words, autoreactive T cells and autoantibody-producing B cells are different from thymus-derived T cells and bone marrow-derived B cells. Activated extrathymic T cells and B-1 cells are often observed in numerous autoimmune diseases, aging, malarial infection and chronic graft-versus-host disease. It is thought that the autoreactivity of extrathymic T cells and B-1 cells may be important for the elimination of "abnormal self" tissues or cells. However, over-activation of innate lymphocytes may be related to the onset of disease or self-tissue destruction. However, it must be emphasized that the autoreactivity of innate lymphocytes is not generated by failure of the thymic pathway of T-cell differentiation or the conventional pathway of B-2 cells.

Induction of ssDNA-binding autoantibody secreting B cell immunity during murine malaria infection is a critical part of the protective immune responses

Although it has been hypothesized that autoimmune-like phenomena may play a critical role in the protective immune responses to both human and animal malaria, there are still no evidence-based data to support this view. In this study we demonstrate that the majority of anti-single stranded (ss) DNA autoantibody secreting B cells were confined to B220(+)CD21(+)CD23(-) cells and that these cells expanded significantly in the spleen of C57BL/6 mice infected with Plasmodium yoelii 17X non-lethal (PyNL). To determine the role of ssDNA-binding autoantibody secreting B cell responses in murine malaria, we conjugated generation 6 (poly) amidoamine dendrimer nanoparticles with ssDNA to deplete ssDNA-binding autoreactive B cells in vivo. Our data revealed that 55.5% of mice died after DNA-coated nanoparticle-mediated in vivo depletion of ssDNA-specific autoreactive B cells and subsequent challenge using PyNL. Adoptive transfer of B cells with ssDNA specificity to mice, followed by PyNL infection, caused a later appearance and inhibition of parasitemia. The possible mechanism by which the ssDNA-binding autoantibody secreting B cells is involved in the protection against murine malaria has also been demonstrated.

Immunologic states of autoimmune diseases

The etiology and immunologic states of autoimmune diseases have mainly been discussed without consideration of extrathymic T cells, which exist in the liver, intestine, and excretion glands. Because extrathymic T cells are autoreactive and are often simultaneously activated along with autoantibody-producing B-1 cells, these extrathymic T cells and B-1 cells should be introduced when considering the immunologic states of autoimmune diseases. The immunologic states of autoimmune diseases resemble those of aging, chronic GVH disease, and malarial infection. Namely, under all these conditions, conventional T and B cells are rather suppressed concomitant with thymic atrophy or involution. In contrast, extrathymic T cells and B-1 cells are inversely activated at this time. These facts suggest that the immunologic states of autoimmune diseases should be reevaluated by introducing the concept of extrathymic T cells and autoantibody-producing B-1 cells, which might be primordial lymphocytes in phylogeny.

Malaria protection in beta 2-microglobulin-deficient mice lacking major histocompatibility complex class I antigens: essential role of innate immunity, including gammadelta T cells

It is still controversial whether malaria protection is mediated by conventional immunity associated with T and B cells or by innate immunity associated with extrathymic T cells and autoantibody-producing B cells. Given this situation, it is important to examine the mechanism of malaria protection in beta(2)-microglobulin-deficient (beta(2)m(-/-)) mice. These mice lack major histocompatibility complex class I and CD1d antigens, which results in the absence of CD8(+) T cells and natural killer T (NKT) cells. When C57BL/6 and beta(2)m(-/-) mice were injected with parasitized (Plasmodium yoelii 17XNL) erythrocytes, both survived from the infection and showed a similar level of parasitaemia. The major expanding T cells were NK1.1(-) alphabeta T-cell receptor(int) cells in both mice. The difference was a compensatory expansion of NK and gammadelta T cells in beta(2)m(-/-) mice, and an elimination experiment showed that these lymphocytes were critical for protection in these mice. These results suggest that malaria protection might be events of the innate immunity associated with multiple subsets with autoreactivity. CD8(+) T and NKT cells may be partially related to this protection.

Protection against malaria due to innate immunity enhanced by low-protein diet

Mice were fed ad libitum with a normal diet (25% protein) or low-protein diets (0-12.5% protein) for a wk and then infected with a nonlethal or lethal strain of Plasmodium yoelii, that is, blood stage infection. The same diet was continued until recovery. Mice fed with a normal diet showed severe parasitemia during nonlethal infection, but survived the infection. They died within 2 wk in the case of lethal infection. However, all mice fed with low-protein diets survived without apparent parasitemia (there were small peaks of parasitemia) in cases of both nonlethal and lethal strains. These surviving mice were found to have acquired potent innate immunity, showing the expansion of NK1.1 -TCRint cells and the production of autoantibodies during malarial infection. Severe combined immunodeficiency (scid) mice, which lack TCRint cells as well as TCRhigh cells, did not survive after malarial infection of lethal strain of P. yoelii, even when low-protein diets were given. These results suggest that low-protein diets enhanced innate immunity and inversely decreased conventional immunity, and that these immunological deviations rendered mice resistant against malaria. The present outcome also reminds us of our experience in the field study of malaria, in which some inhabitants eventually avoided contracting malaria even after apparent malarial infection.

Essential role of extrathymic T cells in protection against malaria

Athymic nude mice carry neither conventional T cells nor NKT cells of thymic origin. However, NK1.1(-)TCR(int) cells are present in the liver and other immune organs of athymic mice, because these lymphocyte subsets are truly of extrathymic origin. In this study, we examined whether extrathymic T cells had the capability to protect mice from malarial infection. Although B6-nu/nu mice were more sensitive to malaria than control B6 mice, these athymic mice were able to survive malaria when a reduced number of parasitized erythrocytes (5 x 10(3) per mouse) were injected. At the fulminant stage, lymphocytosis occurred in the liver and the major expanding lymphocytes were NK1.1(-)TCR(int) cells (IL-2Rbeta(+)TCRalphabeta(+)). Unconventional CD8(+) NKT cells (V(alpha)14(-)) also appeared. Similar to the case of B6 mice, autoantibodies (IgM type) against denatured DNA appeared during malarial infection. Immune lymphocytes isolated from the liver of athymic mice which had recovered from malaria were capable of protecting irradiated euthymic and athymic mice from malaria when cell transfer experiments were conducted. In conjunction with the previous results in euthymic mice, the present results in athymic mice suggest that the major lymphocyte subsets associated with protection against malaria might be extrathymic T cells.

Extrathymic T cells in malaria protection, including evidence for the onset of erythropoiesis in the liver during infection

This review proposes the possibility that malarial protection might not be achieved through the process of acquired immunity in which the constituents are conventional T and B (B-2) cells. On the other hand, malarial protection might be achieved by the process of innate immunity in which the constituents are extrathymic T cells and autoantibody-producing B-1 cells. Accordingly, mice infected with malaria exhibited severe thymic atrophy, and the expansion of IL-2Rbeta+ CD3int cells and its subset of NK1.1-CD3int cells were simultaneously induced. In parallel with the expansion of extrathymic T cells in the liver, extramedullary erythropoiesis was found to begin in the liver of these mice. Interestingly, malarial protozoa were primarily seen in only these nucleated erythrocytes in the liver at the early stage of infection. These results suggest that malaria immunology falls into a new field of immunology, namely, innate immunity. The similarity of the immune states among malaria, aging, and autoimmune diseases also suggest that the immunosuppression of a conventional, acquired immune system is more likely the common mechanism underlying these diseases or physiological responses.

Resistance to malarial infection is achieved by the cooperation of NK1.1(+) and NK1.1(-) subsets of intermediate TCR cells which are constituents of innate immunity

We previously reported that the major expanding lymphocytes were intermediate TCR (TCR(int)) cells (mainly NK1.1(-)) during malarial infection in mice. Cell transfer experiments of TCR(int) cells indicated that these T cells mediated resistance to malaria. However, TCR(int) cells always contain NK1.1(+)TCR(int) cells (i.e., NKT cells) and controversial results (NKT cells were effective or not for resistance to malaria) have been reported by different investigators. In this study, we used CD1d((-/-)) mice, which almost completely lack NKT cells in the liver and other immune organs. Parasitemia was prolonged in the blood of CD1d((-/-)) mice and the expansion of lymphocytes in the liver of these mice was more prominent after an injection of Plasmodium yoelii-infected erythrocytes. However, these mice finally recovered from malaria. In contrast to B6 mice, CD4(-)8(-) NKT cells as well as NK1.1(-)CD3(int) cells expanded in CD1d((-/-)) mice after malarial infection, instead of CD4(+) (and CD8(+)) NKT cells. These newly generated CD4(-)8(-)NKT cells in CD1d((-/-)) mice did not use an invariant chain of Valpha14Jalpha281 for TCRalpha. Other evidence was that severe thymic atrophy and autoantibody production were accompanied by malarial infection, irrespective of the mice used. These results suggest that both NK1.1(-) and NK1.1(+) subsets of TCR(int) cells (i.e., constituents of innate immunity) are associated with resistance to malaria and that an autoimmune-like state is induced during malarial infection.

Autoimmunity and malaria: what are they doing together?

A common feature of autoimmunity is the presence of autoantibodies (AAb). Two types of AAb have been described: the 'pathogenic' AAb, associated with autoimmune diseases (AID), and the so-called 'natural' AAb. The latter are present in all normal individuals and have been postulated to play a major role as a first defensive barrier of the organism. Both the 'pathogenic' and the 'natural' AAb can be detected at higher frequencies among individuals exposed to viral, bacterial and parasitic infections. The malaria associated AAb do not seem to result from a generalised polyclonal B-cell activation (PBA), have specificities that may differ according to the degree of clinical immunity and do not seem to be pathogenic. Malaria may offer a protective effect against AID, by diminishing its severity or by either preventing or retarding its expression. AAb could also participate in the immune protection against malaria, and this could happen in several ways: (i) AAb directed to modified Ag expressed on the red blood cell (RBC) membrane during parasitisation and (ii) AAb reactive with crypto- or neo-Ag revealed on both normal and infected RBC membranes, by destroying infected, and also normal, erythrocytes; (iii) anti-idiotype AAb specific of the binding site of anti-merozoite Ab, which would mimic the parasite ligand for the RBC receptor, by competing with parasites and blocking RBC invasion; (iv) AAb cross-reactive with parasite material - such as nuclear or cytoskeleton Ag - having a direct parasiticide activity; (v) the natural AAb network, through its 'anti-bacterial first defense barrier'; and finally (vi) anti-phospholipid (PL) AAb, by neutralizing the pathogenic properties of parasite-derived PL. Finally, in view of currently available knowledge, it is concluded that, since AAb are not always pathogenic, the price for an 'autoimmunity-mediated' protection in malaria would not necessarily be immunopathology and clinical autoimmunity, and a protective role of AAb could be exerted with no danger to the host.

Is there a role for autoimmunity in immune protection against malaria?

Much remains to be known about the mechanisms involved in protective immunity against malaria and the way it is acquired. This is probably the reason why, in spite of so much progress, it has not yet been possible to develop an anti-malaria vaccine able to induce parasite specific antibodies (Ab) and/or T-cells. It has been considered in the early 80s that the induction of efficient protection against the blood stage forms of Plasmodium falciparum would not be possible without simultaneously eliciting an autoimmune (AI) response against erythrocytes, even at the price of inducing an AI pathology. Despite the description of the reciprocal relationship, i.e. the protective effect of malaria on the development of AI diseases _ demonstrated since 1970 _ no effort has been made to verify the possible involvement of the AI response in protection against malaria.