**3.1 CD1 molecules and regulation of their expression**

There are five distinct CD1 molecules, CD1a, CD1b, CD1c, CD1d and CD1e (Figure 1). Although these different molecules most likely arose from a single common ancestral gene

Innate Lymphocyte Effectors

exogenous and endogenous antigens during infections.

Endogenous glycosphingolipids binding to CD1 include GM1 ganglioside, sulfatide, galactosylceramide, and sphingomyelin (Darmoise et al., 2010; De Libero & Mori, 2003; Franchini et al., 2007; Hegde et al., 2010; Roy et al., 2008). The self-glycosphingolipids are not only important as self-antigens for T cell activation, but their presence may stabilize and promote CD1 expression on the cell surface (De Libero & Mori, 2003). Unlike microbial glycolipids which require processing in the endosomes, glycosphingolipids can directly bind to CD1 molecules expressed on the cell surface and can displace glycolipids already in these surface CD1 molecules (De Libero & Mori, 2003). Although endogenous

(Natural Killer, Natural Killer T and γδ T Cells) in Infection and Myocarditis 221

expressed on these cells and additionally on non-hemopoietic cells including cardiac myocytes and endothelial cells (Blumberg et al., 1995; Exley et al., 2001; Huber et al., 2003) . CD1 molecules structurally resemble class I MHC molecules since they consist of a single polypeptide chain coded by the CD1 gene and are associated with β2 microglobulin. However, antigen presentation more closely resembles class II MHC molecules since antigen loading occurs in the endosome pathway and is TAP independent (Boes et al. , 2009; Brutkiewicz et al., 1995; Odyniec et al., 2004). The CD1 extracellular domain has a deep antigen binding groove containing two to four hydrophobic pockets into which the alkyl lipid tails of antigens are inserted leaving the glycosylated portion available for T cell recognition (Cheng et al., 2006; Zajonc et al., 2003; Zajonc et al., 2008). The cytoplasmic tails of CD1b, CD1c and CD1d contain a tyrosine motif which directs these molecules to the late endosome while the CD1a cytoplasmic tail lacks this motif and directs this molecule to the early endosome. The difference in trafficking of the CD1 molecules may reflect an evolutionary process since bacteria localize to different cellular organelles and expression of CD1 isoforms to distinct endosome compartments should promote maximal capture and presentation of microbial antigens to host immunity (De Libero & Mori, 2003). CD1b presents bacterial lipids including mycobacterial mycolic acids (Beckman et al., 1994), lipoarabinomannan (Sieling et al., 1995), glucose monomycolate (Moody, 2001), and selfglycosphingolipids such as GM1 ganglioside (Shamshiev et al., 2000). CD1a and CD1c present bacterial phospholipids (Beckman et al., 1996). CD1d presents a bacterial sphingolipid from *Sphingomonas* (Kinjo et al., 2005), alphaproteobacterium from *N. aromaticivorans* (Mattner et al., 2008), glycolipids from *B. burgdorferi* (Kinjo et al., 2006), and a self-sphingolipid isogloboside (Mattner et al., 2005). The sphingolipid -galactosylceramide (αGalCer) isolated from marine sponges, is the classical CD1d ligand (Kawano et al., 1997), but CD1d has also been shown to present an α-galactosyl-diacylglycerol of *B. burgdorferi* (BbGL-II) (Kinjo et al., 2008; Kinjo et al., 2006). Evidence for CD1 presentation of viral antigens is sparse despite the fact that CD1-restricted T cells have been shown to respond in various viral infections including HIV, HSV, influenza and picornavirus (De Santo et al., 2008; Exley et al., 2001; Li & Xu, 2008; Yuan et al., 2006). Indeed, it would be highly unlikely that CD1 could directly present picornavirus molecules since these are non-enveloped viruses and should therefore lack any potential for glycolipid or lipopeptide antigens. Possible explanations for CD1-restricted immune responses to viruses exist. For example, infection may promote cellular lipidation of virus proteins (Van Rhijn et al., 2005) or infection may cause increased expression of endogenous glycolipid antigens (De Libero et al., 2005; Paget et al., 2007). Lysosomal α-galactosidase A is an enzyme which degrades endogenous lipid antigens (Darmoise et al., 2010). However, subsequent to many infections, α-galactosidase A activity can be severely curtailed leading to endogenous lipid accumulation. This means that CD1d dependent innate immunity may be directed to both

and are located as a cluster of genes on the same chromosome (De Libero & Mori, 2003), they share only approximately 30% homology and have distinct expression patterns and functional characteristics (Blumberg et al., 1995; Calabi et al., 1989; Kasmar et al., 2009). These proteins belong to a family of non-polymorphic, class I-like major histocompatibility complex (MHC) molecules (Boes et al., 2009). Humans express CD1a, CD1b, CD1c, CD1e (Group 1 CD1 molecules) and CD1d (Group 2 CD1 molecule). Mice express two isoforms of CD1d but lack any of the Group 1 CD1 molecules (Bradbury et al., 1990; Sugita et al., 1999). Other mammals express varying combinations of the different CD1 isoforms. For example, ruminants, such as cattle, express CD1a, three isoforms of CD1b and CD1e but lack either homologues of CD1c or CD1d (Van Rhijn et al., 2006). To date, all mammals have at least one CD1 molecule and a similar CD1-like molecule has been recently found in birds (Dvir et al., 2010). The wide distribution of CD1 expression among species underlines the importance of these molecules in immunity. A major difference between the non-classical CD1 molecules and the classical MHC I and MHC II molecules is that the latter molecules primarily present peptide antigens while CD1 molecules present amphipathic glycolipid (Kasmar et al., 2009; Kulkarni, 2010) and possibly hydrophobic peptide (Van Rhijn et al., 2009) antigens to T cells which provides a more comprehensive sampling of microbial products than the classical MHC molecules alone could provide. There are few CD1 genes (maximum of 12 but not all are present in all species) compared to the classical MHC molecules (>200), and CD1 proteins are highly conserved with few if any allelic variations. However, crystal structure analysis suggests that CD1 proteins have substantial flexibility and can conformationally change to present diverse microbial and self glycolipids (Zajonc et al., 2008).

Fig. 1. CD1 family of non-classical MHC class I-like molecules.

There are five known members of the CD1 family divided into Group 1 and Group 2 molecules. All CD1 molecules present lipid antigens, unlike classical MHC molecules which primarily present peptide antigens. All CD1 genes derive from a common ancestral gene. Unlike the other four members of the CD1 family, CD1e is only found as a soluble form in endosomes where it aids in trimming phosphatidylinositol for presentation by CD1b (de la Salle et al., 2005). CD1a, b, and c molecules are expressed on myeloid cells while CD1d is

and are located as a cluster of genes on the same chromosome (De Libero & Mori, 2003), they share only approximately 30% homology and have distinct expression patterns and functional characteristics (Blumberg et al., 1995; Calabi et al., 1989; Kasmar et al., 2009). These proteins belong to a family of non-polymorphic, class I-like major histocompatibility complex (MHC) molecules (Boes et al., 2009). Humans express CD1a, CD1b, CD1c, CD1e (Group 1 CD1 molecules) and CD1d (Group 2 CD1 molecule). Mice express two isoforms of CD1d but lack any of the Group 1 CD1 molecules (Bradbury et al., 1990; Sugita et al., 1999). Other mammals express varying combinations of the different CD1 isoforms. For example, ruminants, such as cattle, express CD1a, three isoforms of CD1b and CD1e but lack either homologues of CD1c or CD1d (Van Rhijn et al., 2006). To date, all mammals have at least one CD1 molecule and a similar CD1-like molecule has been recently found in birds (Dvir et al., 2010). The wide distribution of CD1 expression among species underlines the importance of these molecules in immunity. A major difference between the non-classical CD1 molecules and the classical MHC I and MHC II molecules is that the latter molecules primarily present peptide antigens while CD1 molecules present amphipathic glycolipid (Kasmar et al., 2009; Kulkarni, 2010) and possibly hydrophobic peptide (Van Rhijn et al., 2009) antigens to T cells which provides a more comprehensive sampling of microbial products than the classical MHC molecules alone could provide. There are few CD1 genes (maximum of 12 but not all are present in all species) compared to the classical MHC molecules (>200), and CD1 proteins are highly conserved with few if any allelic variations. However, crystal structure analysis suggests that CD1 proteins have substantial flexibility and can conformationally change to present diverse microbial and self glycolipids (Zajonc et

al., 2008).

Fig. 1. CD1 family of non-classical MHC class I-like molecules.

There are five known members of the CD1 family divided into Group 1 and Group 2 molecules. All CD1 molecules present lipid antigens, unlike classical MHC molecules which primarily present peptide antigens. All CD1 genes derive from a common ancestral gene. Unlike the other four members of the CD1 family, CD1e is only found as a soluble form in endosomes where it aids in trimming phosphatidylinositol for presentation by CD1b (de la Salle et al., 2005). CD1a, b, and c molecules are expressed on myeloid cells while CD1d is expressed on these cells and additionally on non-hemopoietic cells including cardiac myocytes and endothelial cells (Blumberg et al., 1995; Exley et al., 2001; Huber et al., 2003) . CD1 molecules structurally resemble class I MHC molecules since they consist of a single polypeptide chain coded by the CD1 gene and are associated with β2 microglobulin. However, antigen presentation more closely resembles class II MHC molecules since antigen loading occurs in the endosome pathway and is TAP independent (Boes et al. , 2009; Brutkiewicz et al., 1995; Odyniec et al., 2004). The CD1 extracellular domain has a deep antigen binding groove containing two to four hydrophobic pockets into which the alkyl lipid tails of antigens are inserted leaving the glycosylated portion available for T cell recognition (Cheng et al., 2006; Zajonc et al., 2003; Zajonc et al., 2008). The cytoplasmic tails of CD1b, CD1c and CD1d contain a tyrosine motif which directs these molecules to the late endosome while the CD1a cytoplasmic tail lacks this motif and directs this molecule to the early endosome. The difference in trafficking of the CD1 molecules may reflect an evolutionary process since bacteria localize to different cellular organelles and expression of CD1 isoforms to distinct endosome compartments should promote maximal capture and presentation of microbial antigens to host immunity (De Libero & Mori, 2003). CD1b presents bacterial lipids including mycobacterial mycolic acids (Beckman et al., 1994), lipoarabinomannan (Sieling et al., 1995), glucose monomycolate (Moody, 2001), and selfglycosphingolipids such as GM1 ganglioside (Shamshiev et al., 2000). CD1a and CD1c present bacterial phospholipids (Beckman et al., 1996). CD1d presents a bacterial sphingolipid from *Sphingomonas* (Kinjo et al., 2005), alphaproteobacterium from *N. aromaticivorans* (Mattner et al., 2008), glycolipids from *B. burgdorferi* (Kinjo et al., 2006), and a self-sphingolipid isogloboside (Mattner et al., 2005). The sphingolipid -galactosylceramide (αGalCer) isolated from marine sponges, is the classical CD1d ligand (Kawano et al., 1997), but CD1d has also been shown to present an α-galactosyl-diacylglycerol of *B. burgdorferi* (BbGL-II) (Kinjo et al., 2008; Kinjo et al., 2006). Evidence for CD1 presentation of viral antigens is sparse despite the fact that CD1-restricted T cells have been shown to respond in various viral infections including HIV, HSV, influenza and picornavirus (De Santo et al., 2008; Exley et al., 2001; Li & Xu, 2008; Yuan et al., 2006). Indeed, it would be highly unlikely that CD1 could directly present picornavirus molecules since these are non-enveloped viruses and should therefore lack any potential for glycolipid or lipopeptide antigens. Possible explanations for CD1-restricted immune responses to viruses exist. For example, infection may promote cellular lipidation of virus proteins (Van Rhijn et al., 2005) or infection may cause increased expression of endogenous glycolipid antigens (De Libero et al., 2005; Paget et al., 2007). Lysosomal α-galactosidase A is an enzyme which degrades endogenous lipid antigens (Darmoise et al., 2010). However, subsequent to many infections, α-galactosidase A activity can be severely curtailed leading to endogenous lipid accumulation. This means that CD1d dependent innate immunity may be directed to both exogenous and endogenous antigens during infections.

Endogenous glycosphingolipids binding to CD1 include GM1 ganglioside, sulfatide, galactosylceramide, and sphingomyelin (Darmoise et al., 2010; De Libero & Mori, 2003; Franchini et al., 2007; Hegde et al., 2010; Roy et al., 2008). The self-glycosphingolipids are not only important as self-antigens for T cell activation, but their presence may stabilize and promote CD1 expression on the cell surface (De Libero & Mori, 2003). Unlike microbial glycolipids which require processing in the endosomes, glycosphingolipids can directly bind to CD1 molecules expressed on the cell surface and can displace glycolipids already in these surface CD1 molecules (De Libero & Mori, 2003). Although endogenous

Innate Lymphocyte Effectors

(Natural Killer, Natural Killer T and γδ T Cells) in Infection and Myocarditis 223

important in pathogenesis. CD1d-restricted effectors are cytolytic to CVB3 infected cardiocytes in vitro and expression of CD1d on infected cardiocytes in vivo may contribute directly to their death through cytolytic T lymphocyte activity. To address this question, bone marrow transplantation was performed between wild-type (CD1d+/+) and CD1d-/ mice where either the hemopoeitic cells were CD1d+ and the non-hemopoeitic cells (heart) was CD1d- or the opposite (Huber, 2006). These studies showed that CD1d expression on both hemopoeitic and non-hemopoeitic cells contributed to heart disease, although CD1d expression on hemopoeitic cells was of primary importance. There are no published studies showing the importance of CD1in clinical myocarditis. It is therefore not possible to evaluate the significance of CD1-dependent innate immunity in the human disease. However, based on the tight control of CD1 for pathogenesis in the experimental disease, the strong association between various microbial infections and clinical myocarditis, and the importance of CD1-restricted immunity in many different microbial infections; future

Many T cells respond to CD1 molecules (Barral & Brenner, 2007; Kaufmann, 1996) and express either T cell receptors (TCR) consisting of α/β or γ/δ polypeptide chains. Group 1 CD1-restricted αβ T cells are clonally diverse with fine antigen specificity, recognition of both self and foreign lipid antigens and either double negative (CD4-CD8-) or single positive (CD4+ or CD8+) (Barral & Brenner, 2007; Kaufmann, 1996; Vincent et al., 2005). The αβ T cell response is slow, similar to classical MHC αβ T cell responses indicating that these CD1-restricted effectors probably do not belong to the innate immune system. There are two major populations of γδ T cells in humans (Vδ1 and Vδ2) with Vδ2 cells primarily present in the circulation and Vδ1 cells primarily found in tissues and intestine (Das et al., 2004). Subsets of both γδ populations recognize antigens in context of non-classical MHC class Ilike molecules including group 1 CD1(Rincon-Orozco et al., 2005; Russano et al., 2007). Activation of the group 1 CD1 restricted effectors requires IL-12, NKG2D activation on the effector and adhesion molecule interactions (LFA3/CD2, LFA1/ICAM1) in addition to TCR engagement. Since mice lack Group 1 CD1 molecules, this species does not have Group 1

investigation into a role for CD1 in this disease would be warranted.

CD1-restricted immunity. However, these effectors may function in humans.

T cells reacting to CD1d (Group 2 CD1) are also diverse. CD1d-restricted natural killer T (NKT) cells are designated as either invariant NKT (iNKT, also known as Type 1) or diverse NKT (also known as Type 2) cells (Barral & Brenner, 2007; Kronenberg, 2005; Ronchi & Falcone, 2008; Taniguchi et al., 2010). Type 1 iNKT cells have a TCR comprised of a single type of TCRα chain (Vα14Jα18 for mice and Vα24Jα18 for humans) and one of a limited number of distinct TCRβ chains resulting in limited clonal diversity. In contrast, Type 2 NKT cells use TCR comprised of diverse α and β chains. iNKT cells comprise between 2-40% of CD3+ cells in various tissues (Bendelac et al., 2007; Terabe & Berzofsky, 2008), have a constitutively activated phenotype, and rapidly secret large amounts of cytokines (IFN-γ, IL-4, IL-17, IL-5, and IL-13) upon activation due to the presence of pre-formed cytokine mRNA in the cells (Kronenberg, 2005; Michel, 2007; Olson et al., 2009; Stetson et al., 2003). Three mechanisms of iNKT cell activation have been described (Figure 2). Direct activation involves recognition of microbial antigens presented by CD1d on antigen presenting cells (TCR-mediated). In contrast, indirect activation either involves microbial stimulation of antigen presenting cells to release cytokines (IL-12 and Type 1 IFN) and presentation of

**3.2 Natural killer T cells and CD1-restricted γδ T cells** 

glycosphingolipids have been primarily viewed as the probable self antigen in CD1 dependent immunity, recent studies by Pei et al (Pei et al., 2010) demonstrated that cell lines incapable of glycosphingolipid biosynthesis were nonetheless capable of activating CD1 restricted cells. Thus, the types of self antigen capable of activating the CD1-dependent innate immune response are likely to be broader than originally thought.

Group 1 CD1 molecules are not expressed on monocytes in the blood and recent studies have shown that serum immunoglobulin and lipids suppress expression of these molecules (Leslie et al., 2008; Smed-Sorensen et al., 2008). However, once monocytes leave the circulation, Group 1 CD1 molecules can be induced by signaling through TLR2 (Roura-Mir et al., 2005), TLR2/TLR5 agonists, or cytokines (GM-CSF and IL-4) (Moody, 2006). CD1d is not up-regulated by GM-CSF and IL-4 (Exley et al., 2001; Sallusto & Lanzavecchia, 1994). CD1d is constitutively expressed in dendritic cells, monocytes and macrophage, but levels can be further increased subsequent to infection (Dougan et al. , 2007; Durante-Mangoni et al., 2004; Huber et al., 2003; Skold & Behar, 2003). Such up-regulation depends upon signaling through TLR and cytokines (IFNγ, IFNβ, TNFα) (Raghuraman et al., 2006; Skold et al., 2005). While microbial infections can up-regulate CD1 expression, they can also result in CD1 down-regulation (Donovan et al., 2007; Raftery et al., 2006). Viruses are well-known for their ability to evade immunity through multiple different mechanisms (Alcami & Koszinowski, 2000; Antoniou & Powis, 2008; Vossen et al., 2002). While most investigations of immune evasion by viruses center on the adaptive immune response, viruses also interfere with innate immunity. The HIV Nef protein binds to CD1d decreasing CD1d transport to the cell surface (Hage et al., 2005). Similarly, HSV, suppresses CD1 expression by interrupting the CD1 recycling pathway (Yuan et al., 2006). Karposi sarcoma-associated herpesvirus (KSHV) uses its modulator of immune recognition (MIR) proteins to ubiquitinize the cytoplastic tail of the CD1d molecule leading to its endocytosis (Sanchez et al., 2005). Activation of TLR7/8 blocks CD1 expression at the protein and mRNA levels (Assier et al., 2007). Finally, infection can change the endosomal processing of glycolipids which could restrict antigen availability to CD1 molecules.

Unlike Group 1 CD1 molecules, CD1d can be expressed on non-hemopoeitic cells (Huber et al., 2003; Monzon-Casanova et al. ; Sikder et al., 2009) CVB3 infection augments CD1d expression on macrophage, dendritic cells and T cells (Huber, 2006). The virus also causes de novo CD1d expression on non-hemopoietic cells (cardiac endothelial cells and myocytes), but only in non-hemopoietic cells actively replicating virus. Uninfected myocytes/endothelial cells immediately adjacent to infected cells remain CD1d negative (Huber et al., 2003). The requirement for active virus replication strongly suggests that TLR signal pathways such as TLR3 (recognizing single stranded RNA) or TLR7/8 (recognizing double stranded RNA) are necessary. However, virus replication alone is insufficient. Mice or cells infected with a non-pathogenic variant of CVB3, H310A1 (Knowlton et al., 1996), fail to up-regulate CD1d either on hemopoeitic or non-hemopoeitic cells (Huber et al., 2003; Huber & Sartini, 2005b). A major difference between the non-pathogenic and pathogenic (H3) variants of CVB3 is that the pathogenic virus is a potent inducer of TNFα. Further studies showed that TNFα and H310A1 infection up-regulated CD1d expression whereas either TNFα or H310A1 infection alone did not. In the mouse model of CVB3 induced myocarditis, CD1d is required for cardiac inflammation and injury. Mice lacking CD1d fail to develop myocarditis despite high levels of virus replication in the heart (Huber et al., 2003). Since CD1d is up-regulated on both hemopoeitic and non-hemopoeitic cells subsequent to CVB3 infection, a major question is where expression of this molecule is most

glycosphingolipids have been primarily viewed as the probable self antigen in CD1 dependent immunity, recent studies by Pei et al (Pei et al., 2010) demonstrated that cell lines incapable of glycosphingolipid biosynthesis were nonetheless capable of activating CD1 restricted cells. Thus, the types of self antigen capable of activating the CD1-dependent

Group 1 CD1 molecules are not expressed on monocytes in the blood and recent studies have shown that serum immunoglobulin and lipids suppress expression of these molecules (Leslie et al., 2008; Smed-Sorensen et al., 2008). However, once monocytes leave the circulation, Group 1 CD1 molecules can be induced by signaling through TLR2 (Roura-Mir et al., 2005), TLR2/TLR5 agonists, or cytokines (GM-CSF and IL-4) (Moody, 2006). CD1d is not up-regulated by GM-CSF and IL-4 (Exley et al., 2001; Sallusto & Lanzavecchia, 1994). CD1d is constitutively expressed in dendritic cells, monocytes and macrophage, but levels can be further increased subsequent to infection (Dougan et al. , 2007; Durante-Mangoni et al., 2004; Huber et al., 2003; Skold & Behar, 2003). Such up-regulation depends upon signaling through TLR and cytokines (IFNγ, IFNβ, TNFα) (Raghuraman et al., 2006; Skold et al., 2005). While microbial infections can up-regulate CD1 expression, they can also result in CD1 down-regulation (Donovan et al., 2007; Raftery et al., 2006). Viruses are well-known for their ability to evade immunity through multiple different mechanisms (Alcami & Koszinowski, 2000; Antoniou & Powis, 2008; Vossen et al., 2002). While most investigations of immune evasion by viruses center on the adaptive immune response, viruses also interfere with innate immunity. The HIV Nef protein binds to CD1d decreasing CD1d transport to the cell surface (Hage et al., 2005). Similarly, HSV, suppresses CD1 expression by interrupting the CD1 recycling pathway (Yuan et al., 2006). Karposi sarcoma-associated herpesvirus (KSHV) uses its modulator of immune recognition (MIR) proteins to ubiquitinize the cytoplastic tail of the CD1d molecule leading to its endocytosis (Sanchez et al., 2005). Activation of TLR7/8 blocks CD1 expression at the protein and mRNA levels (Assier et al., 2007). Finally, infection can change the endosomal processing of glycolipids

Unlike Group 1 CD1 molecules, CD1d can be expressed on non-hemopoeitic cells (Huber et al., 2003; Monzon-Casanova et al. ; Sikder et al., 2009) CVB3 infection augments CD1d expression on macrophage, dendritic cells and T cells (Huber, 2006). The virus also causes de novo CD1d expression on non-hemopoietic cells (cardiac endothelial cells and myocytes), but only in non-hemopoietic cells actively replicating virus. Uninfected myocytes/endothelial cells immediately adjacent to infected cells remain CD1d negative (Huber et al., 2003). The requirement for active virus replication strongly suggests that TLR signal pathways such as TLR3 (recognizing single stranded RNA) or TLR7/8 (recognizing double stranded RNA) are necessary. However, virus replication alone is insufficient. Mice or cells infected with a non-pathogenic variant of CVB3, H310A1 (Knowlton et al., 1996), fail to up-regulate CD1d either on hemopoeitic or non-hemopoeitic cells (Huber et al., 2003; Huber & Sartini, 2005b). A major difference between the non-pathogenic and pathogenic (H3) variants of CVB3 is that the pathogenic virus is a potent inducer of TNFα. Further studies showed that TNFα and H310A1 infection up-regulated CD1d expression whereas either TNFα or H310A1 infection alone did not. In the mouse model of CVB3 induced myocarditis, CD1d is required for cardiac inflammation and injury. Mice lacking CD1d fail to develop myocarditis despite high levels of virus replication in the heart (Huber et al., 2003). Since CD1d is up-regulated on both hemopoeitic and non-hemopoeitic cells subsequent to CVB3 infection, a major question is where expression of this molecule is most

innate immune response are likely to be broader than originally thought.

which could restrict antigen availability to CD1 molecules.

important in pathogenesis. CD1d-restricted effectors are cytolytic to CVB3 infected cardiocytes in vitro and expression of CD1d on infected cardiocytes in vivo may contribute directly to their death through cytolytic T lymphocyte activity. To address this question, bone marrow transplantation was performed between wild-type (CD1d+/+) and CD1d-/ mice where either the hemopoeitic cells were CD1d+ and the non-hemopoeitic cells (heart) was CD1d- or the opposite (Huber, 2006). These studies showed that CD1d expression on both hemopoeitic and non-hemopoeitic cells contributed to heart disease, although CD1d expression on hemopoeitic cells was of primary importance. There are no published studies showing the importance of CD1in clinical myocarditis. It is therefore not possible to evaluate the significance of CD1-dependent innate immunity in the human disease. However, based on the tight control of CD1 for pathogenesis in the experimental disease, the strong association between various microbial infections and clinical myocarditis, and the importance of CD1-restricted immunity in many different microbial infections; future investigation into a role for CD1 in this disease would be warranted.
