Mast Cells Exert Effects Outside the Central Nervous System to Influence Experimental Allergic Encephalomyelitis Disease Course

Mast cells are critical mediators of vaccine-induced Helicobacter clearance in the mouse model

BACKGROUND & AIMS

Despite the proven ability of immunization to prevent Helicobacter infection in mouse models, the precise mechanism of protection has remained elusive.

METHODS

We explored the cellular events associated with Helicobacter clearance from the stomach following vaccination by flow cytometry analysis and histological and molecular studies.

RESULTS

Kinetic studies showed that the infection is undetectable in vaccinated mice at day 5 postbacterial challenge. Flow cytometry analysis showed that the percentages of mast cells (CD3 - CD117 + ) increased in the lymphoid cells isolated from the stomach at day 4 postchallenge in urease + cholera toxin (CT)-vaccinated mice in comparison with mice administered with CT alone (9.4% +/- 4.4% and 3.1% +/- 1%, respectively, for vaccinated and CT administered, n = 5; P < .01). Quantitative PCR analysis showed an increased messenger RNA (mRNA) expression of the mast cell proteases 1 and 2 at day 5 postchallenge in the stomach of vaccinated mice. In contrast to wild-type mice, mast cell-deficient mice (W/W v mice) were not protected from H felis colonization after vaccination. Indeed only 1 out of 12 vaccinated W/W v mice showed a negative urease test. Remarkably, vaccinated W/W v mice reconstituted with cultured bone marrow-derived mast cells recovered the ability to clear the infection after vaccination (8 out of 10 mast cell-reconstituted mice showed negative urease tests [ P < .006 as compared with wild-type mice]).

CONCLUSIONS

These experiments show that mast cells are, unexpectedly, critical mediators of anti- Helicobacter vaccination.

Mast cells as "tunable" effector and immunoregulatory cells: recent advances

This review focuses on recent progress in our understanding of how mast cells can contribute to the initiation, development, expression, and regulation of acquired immune responses, both those associated with IgE and those that are apparently expressed independently of this class of Ig. We emphasize findings derived from in vivo studies in mice, particularly those employing genetic approaches to influence mast cell numbers and/or to alter or delete components of pathways that can regulate mast cell development, signaling, or function. We advance the hypothesis that mast cells not only can function as proinflammatory effector cells and drivers of tissue remodeling in established acquired immune responses, but also may contribute to the initiation and regulation of such responses. That is, we propose that mast cells can also function as immunoregulatory cells. Finally, we show that the notion that mast cells have primarily two functional configurations, off (or resting) or on (or activated for extensive mediator release), markedly oversimplifies reality. Instead, we propose that mast cells are "tunable," by both genetic and environmental factors, such that, depending on the circumstances, the cell can be positioned phenotypically to express a wide spectrum of variation in the types, kinetics, and/or magnitude of its secretory functions.

Leukotriene B4, an activation product of mast cells, is a chemoattractant for their progenitors

Mast cells are tissue-resident cells with important functions in allergy and inflammation. Pluripotential hematopoietic stem cells in the bone marrow give rise to committed mast cell progenitors that transit via the blood to tissues throughout the body, where they mature. Knowledge is limited about the factors that release mast cell progenitors from the bone marrow or recruit them to remote tissues. Mouse femoral bone marrow cells were cultured with IL-3 for 2 wk and a range of chemotactic agents were tested on the c-kit(+) population. Cells were remarkably refractory and no chemotaxis was induced by any chemokines tested. However, supernatants from activated mature mast cells induced pronounced chemotaxis, with the active principle identified as leukotriene (LT) B(4). Other activation products were inactive. LTB(4) was highly chemotactic for 2-wk-old cells, but not mature cells, correlating with a loss of mRNA for the LTB(4) receptor, BLT1. Immature cells also accumulated in vivo in response to intradermally injected LTB(4). Furthermore, LTB(4) was highly potent in attracting mast cell progenitors from freshly isolated bone marrow cell suspensions. Finally, LTB(4) was a potent chemoattractant for human cord blood-derived immature, but not mature, mast cells. These results suggest an autocrine role for LTB(4) in regulating tissue mast cell numbers.

Mast cells and autoimmunity

Mast cells (MCs) are major effector cells in allergic diseases. Recently, it has become evident that the contribution of MCs extends far beyond their accepted role in allergic disease, and that they play a more extensive role in a variety of non-allergic immune processes such as the innate immunity response. These cells have a key role in both the induction and elicitation of several autoimmune conditions. Targeting MC development, maturation or activation may be of value in future prevention and treatment of autoimmune conditions.

Tissue-selective mast cell reconstitution and differential lung gene expression in mast cell-deficient Kit(W-sh)/Kit(W-sh) sash mice

BACKGROUND

Mast cell-deficient Kit(W)/Kit(W-v) mice are an important resource for studying mast cell functions in vivo. However, because they are compound heterozygotes in a mixed genetic background and are infertile, they cannot be crossed easily with other mice.

OBJECTIVE

To overcome this limitation, we explored the use of Kit(W-sh)/Kit(W-sh) mice for studying mast cell biology in vivo.

RESULTS

These mice are in a C57BL/6 background, are fertile and can be bred directly with other genetically modified mice. Ten-week-old Kit(W-sh)/Kit(W-sh) are profoundly mast cell-deficient. No mast cells are detected in any major organ, including the lung. Gene microarrays detect differential expression of just seven of 16,463 genes in lungs of Kit(W-sh)/Kit(W-sh) mice compared with wild-type mice, indicating that resting mast cells regulate expression of a small set of genes in the normal lung. Injecting 10(7) bone marrow-derived mast cells (BMMC) into tail veins of Kit(W-sh)/Kit(W-sh) mice reconstitutes mast cell populations in lung, stomach, liver, inguinal lymph nodes, and spleen, but not in the tongue, trachea or skin. Injection of BMMC into ear dermis or peritoneum reconstitutes mast cells locally in these tissues. When splenectomized Kit(W-sh)/Kit(W-sh) mice are intravenously injected with BMMC, mast cells circulate longer and are found more often in the liver and inguinal lymph nodes, indicating that the spleen acts as a reservoir for mast cells following injection and limits migration to some tissues.

CONCLUSION

In summary, these findings show that mast cell-deficient Kit(W-sh)/Kit(W-sh) mice possess unique attributes that favour their use for studying mast cell functions in vivo.

Mast cells in the development of adaptive immune responses

Mast cells are so widely recognized as critical effector cells in allergic disorders and other immunoglobulin E-associated acquired immune responses that it can be difficult to think of them in any other context. However, mast cells also can be important as initiators and effectors of innate immunity. In addition, mast cells that are activated during innate immune responses to pathogens, or in other contexts, can secrete products and have cellular functions with the potential to facilitate the development, amplify the magnitude or regulate the kinetics of adaptive immune responses. Thus, mast cells may influence the development, intensity and duration of adaptive immune responses that contribute to host defense, allergy and autoimmunity, rather than simply functioning as effector cells in these settings.

Mast cells play a pivotal role in ischaemia reperfusion injury to skeletal muscles

Ischaemia reperfusion (IR) injury is a serious complication of cardiovascular disease, transplantation and replantation surgery. Once established there is no effective method of treatment. Although studies using mast cell-depleted (Wf/Wf) mice implicate mast cells in this pathology, they do not exclude a contribution by other deficiencies expressed in Wf/Wf mice. In order to obtain conclusive evidence for the role of mast cells, we engrafted cultured bone marrow-derived mast cells (BMMC) from normal mice into their Wf/Wf littermates. After 12 weeks, the hind limbs of Wf/Wf, engrafted Wf/Wf and normal littermates were subjected to IR injury. Muscle viability was assessed by both morphology and by nitroblue tetrazolium histochemical assay. Here, we present conclusive evidence for a causal role of mast cells in IR injury. Our data show that muscles from Wf/Wf mice subjected to IR have a significantly greater proportion of viable fibres than normal littermates subjected to identical injury (78.9+/-5.2 vs 27.2+/-3.7%, respectively). When Wf/Wf IR-resistant mice were engrafted with BMMC from normal littermates and subjected to IR, the proportion of viable muscle fibres was significantly reduced (78.9+/-5.2 vs 37.0+/-6.5%). Thus, engraftment of BMMC into Wf/Wf mice restores the susceptibility of skeletal muscle to IR injury irrespective of other abnormalities in Wf/Wf mice. In this model, the numerical density of mast cells undergoes a significant decrease within 1 h of reperfusion, indicating extensive mast cell degranulation. We conclude that mast cells are pivotal effector cells in the pathogenesis of IR injury of murine skeletal muscle.

Elaborate interactions between the immune and nervous systems

The immune system and the nervous system maintain extensive communication, including 'hardwiring' of sympathetic and parasympathetic nerves to lymphoid organs. Neurotransmitters such as acetylcholine, norepinephrine, vasoactive intestinal peptide, substance P and histamine modulate immune activity. Neuroendocrine hormones such as corticotropin-releasing factor, leptin and alpha-melanocyte stimulating hormone regulate cytokine balance. The immune system modulates brain activity, including body temperature, sleep and feeding behavior. Molecules such as the major histocompatibility complex not only direct T cells to immunogenic molecules held in its cleft but also modulate development of neuronal connections. Neurobiologists and immunologists are exploring common ideas like the synapse to understand properties such as memory that are shared in these two systems.