Altered hepatic transport of immunoglobulin A in mice lacking the J chain

We have created J chain knockout mice to define the physiologic role of the J chain in immunoglobulin synthesis and transport. The J chain is covalently associated with pentameric immunoglobulin (Ig) M and dimeric IgA and is also expressed in most IgG-secreting cells. J chain-deficient mice have normal serum IgM and IgG levels but markedly elevated serum IgA. Although polymeric IgA was present in the mutant mice, a larger proportion of their serum IgA was monomeric than was found in wild-type mouse serum. Bile and fecal IgA levels were decreased in J chain-deficient mice compared with wild-type mice, suggesting inefficient transport of J chain-deficient IgA by hepatic polymeric immunoglobulin receptors (pIgR). The pIgR-mediated transport of serum-derived IgA from wild-type and mutant mice was assessed in Madin-Darby canine kidney (MDCK) cells transfected with the pIgR. These studies revealed selective transport by pIgR-expressing MDCK cells of wild-type IgA but not J chain-deficient IgA. We conclude that although the J chain is not required for IgA dimerization, it does affect the efficiency of polymerization or have a role in maintaining IgA dimer stability. Furthermore, the J chain is essential for efficient hepatic pIgR transport of IgA.

Induction of the FK506-binding protein, FKBP13, under conditions which misfold proteins in the endoplasmic reticulum

In order to determine whether the endoplasmic reticulum (ER) luminal FK506-binding protein, FKBP13, shares properties of ER molecular chaperones, MDCK cells were treated with either tunicamycin or Ca2+ ionophores. By Northern-blot analysis, tunicamycin resulted in a 2-fold rise in FKBP13 mRNA, whereas ionophores (A23187 and ionomycin) caused a more impressive rise in FKBP13 mRNA (up to 5-fold with ionomycin). Actinomycin D chase experiments in ionomycin-treated cells revealed no change in the half-life of FKBP13 mRNA, indicating that the increase in FKBP13 mRNA observed was not due to greater message stability. Moreover, sequencing of the 5' flanking region of the gene for murine FKBP13 revealed significant similarity to similar regions in human BiP (immunoglobulin-binding protein) and the human glucose-regulated protein grp94, including a 37 bp sequence in FKBP13 with approximately 50% identity with the unfolded protein response element of the BiP gene. Together, these data suggest a role for FKBP13 in ER protein folding.

Increased type 1 fimbrial expression among commensal Escherichia coli isolates in the murine cecum following catabolic stress

Although indigenous bacteria intimately colonize the intestinal mucosa, under normal conditions the intestinal epithelial cell is free of adherent bacteria. Nonetheless, commensal bacteria such as Escherichia coli adhere to and translocate across the intestinal epithelium in association with a number of pathologic states including hemorrhagic shock, immunosuppression, traumatic tissue injury, and lack of enteral feedings. The adhesins involved in the adherence of indigenous E. coli to the intestinal epithelium in vivo following catabolic stress are unknown. We have developed a mouse model to study the bacterial adhesins which mediate the increased intestinal adherence of E. coli after partial hepatectomy and short-term starvation. Our studies demonstrated that hepatectomy and starvation in the mouse were associated with a 7,500-fold increase in the numbers of E. coli bacteria adhering to the cecum. In addition, erythrocyte agglutination studies, as well as immunostaining of fimbrial preparations and electron micrographs of the bacteria, revealed that surface type 1 fimbriae were more abundant in the commensal E. coli harvested from the ceca of the stressed mice. These E. coli isolates adhered to a mouse colon cell line and injected cecal loops in a mannose-inhibitable manner, which suggests a role for type 1 fimbriae in the adherence of the E. coli isolates to the cecum in vivo following host catabolic stress.

Surgical stress shifts the intestinal Escherichia coli population to that of a more adherent phenotype: role in barrier regulation

BACKGROUND

We have shown that the combination of surgical stress and starvation in mice is associated with a defect in epithelial permeability and increased numbers of mucosa-associated Escherichia coli in the cecum. The aim of this study was to determine the specific role of mucosa-associated E coli on epithelial barrier dysfunction in this model.

METHODS

Cecal E coli were harvested from mice 48 hours after a sham operation (control mice) or after a 30% surgical hepatectomy with only water provided ad libitum (short-term starvation) after the surgical procedure. Strains were tested for their ability to adhere to and alter the transepithelial electrical resistance (TEER) of cultured young adult mouse colon epithelial cells. TEER changes were further characterized by mannitol fluxes to confirm a defect in paracellular permeability.

RESULTS

Strains of cecal E coli harvested from hepatectomy-starved mice adhered to and altered the permeability of young adult mouse colon cells, whereas E coli from the cecum of control mice were less adherent and had no effect on epithelial permeability. The effect of the strains harvested from mice after hepatectomy on the TEER of young adult mouse colon cells was inhibited by mannose and reversed by ciprofloxacin.

CONCLUSION

The combination of surgical stress and short-term starvation is associated with a greater abundance of adherent and barrier-altering strains of E coli in the mouse cecum.

Decreased vaginal disease in J-chain-deficient mice following herpes simplex type 2 genital infection

J-chain-deficient (Jch(-/-)) mice were used to study the role of polymeric IgA (pIgA) in primary disease and protective immunity following genital herpes simplex type 2 (HSV-2) infection. Vaginal IgA in the Jch(-/-) mice was composed primarily of monomeric IgA and was not associated with secretory component (SC). In contrast, vaginal IgA in wild-type (WT) mice was predominantly polymeric and bound to SC. Following HSV-2 genital infection, the Jch(-/-) mice consistently exhibited fewer vaginal symptoms (P = 0.010) and mortality (P = 0.075) than did the WT mice. The variation in disease expression could not be explained by differences in local viral replication, since titers in vaginal wash fluid were comparable. To assess the effect of J chain deficiency on protective immunity, WT and Jch(-/-) mice were immunized intravaginally with attenuated HSV-2, challenged intravaginally with wild-type virus 5 weeks later, and evaluated for vaginal infection and neurological disease. Although the Jch(-/-) mice had reduced vaginal HSV-specific IgA and IgG levels following immunization, both WT and Jch(-/-) mice were protected from symptoms following wild-type virus challenge. We conclude that pIgA is not required for protective immunity against genital HSV-2 disease and that J chain deficiency offers some protection against symptoms following primary HSV-2 genital infection.

Structural organization of the genes encoding human and murine FK506-binding protein (FKBP) 13 and comparison to FKBP1

FK506-binding protein (FKBP)12 and FKBP13 are members of a family of proteins which bind the immunosuppressant drugs, FK506 and rapamycin. FKBP12 and FKBP13 are encoded by distinct genes, designated FKBP1 and FKBP2, respectively. The structure of human FKBP1 was previously characterized. We now report the genomic structure of the human and murine FKBP2 genes. Comparison of FKBP1 and FKBP2 reveals significant homology and correlation of intron positions in the C-terminal region, suggesting that these genes may have evolved from a common ancestral gene.

Lack of association of secretory component with IgA in J chain-deficient mice

J chain has been proposed to play a role in the mucosal transport of polymeric Igs (pIg) by the polymeric Ig receptor (pIgR). We have previously reported the generation of J chain-deficient mice. These mice exhibited elevated serum IgA and depleted biliary and fecal IgA levels compared with wild-type mice. We report here that, unlike the IgA levels in bile and feces, IgA levels in local mucosal and glandular secretions were not depressed in J chain-deficient mice. Breast milk, intestinal mucosal surface, and nasal wash IgA levels in the mutant mice were similar to wild-type mice while bronchoalveolar lavage IgA levels were higher in the J chain-deficient animals. Western blot analysis with an Ab to secretory component (SC), the portion of the pIgR that remains bound to pig in secretions, and immunoprecipitation with Abs directed against IgA showed that secreted IgA was associated with SC in wild-type but not J chain-deficient mice. The IgA in wild-type secretions was polymeric while the secretions of J chain-deficient mice contained IgA monomers and other nonpolymeric IgA forms. Thus, J chain is not essential for IgA transport by intestinal, mammary, or respiratory epithelia but is necessary for the stable association of pIgA with SC. Further, we suggest that J chain-deficient IgA is transported into secretions by a different mechanism than wild-type IgA.

Lack of association of secretory component with IgA in J chain-deficient mice

J chain has been proposed to play a role in the mucosal transport of polymeric Igs (pIg) by the polymeric Ig receptor (pIgR). We have previously reported the generation of J chain-deficient mice. These mice exhibited elevated serum IgA and depleted biliary and fecal IgA levels compared with wild-type mice. We report here that, unlike the IgA levels in bile and feces, IgA levels in local mucosal and glandular secretions were not depressed in J chain-deficient mice. Breast milk, intestinal mucosal surface, and nasal wash IgA levels in the mutant mice were similar to wild-type mice while bronchoalveolar lavage IgA levels were higher in the J chain-deficient animals. Western blot analysis with an Ab to secretory component (SC), the portion of the pIgR that remains bound to pig in secretions, and immunoprecipitation with Abs directed against IgA showed that secreted IgA was associated with SC in wild-type but not J chain-deficient mice. The IgA in wild-type secretions was polymeric while the secretions of J chain-deficient mice contained IgA monomers and other nonpolymeric IgA forms. Thus, J chain is not essential for IgA transport by intestinal, mammary, or respiratory epithelia but is necessary for the stable association of pIgA with SC. Further, we suggest that J chain-deficient IgA is transported into secretions by a different mechanism than wild-type IgA.

Mechanisms of heterosubtypic immunity to lethal influenza A virus infection in fully immunocompetent, T cell-depleted, beta2-microglobulin-deficient, and J chain-deficient mice

Immunity that is cross-protective between different influenza A virus subtypes (termed heterosubtypic immunity) can be demonstrated readily in some animals but only rarely in humans. Induction of heterosubtypic immunity in humans by vaccines would provide public health benefit, perhaps offering some protection against pandemics or other new influenza A strains. Therefore, we studied mechanisms mediating heterosubtypic immunity in mice. Immunization with either A/H1N1 or A/H3N2 virus protected mice against mortality following heterosubtypic challenge while providing modest reductions in lung virus titers. No cross-protection was seen with distantly related type B influenza virus. Depletion of CD4+ or CD8+ T cells or both around the time of challenge had no significant effect on survival, indicating that these cells are not required at the effector stage. beta2-microglobulin knockout mice could be protected readily against heterosubtypic challenge, confirming that class I-restricted T cells are not required. In beta2-microglobulin -/- mice, depletion of CD4+ T cells partially abrogated heterosubtypic immunity, showing that they play a role in these mice. Passive transfer of Abs to naive recipients protected against subsequent challenge with homologous but not heterosubtypic virus. Because a role for secretory Abs has been suggested, we studied dependence on the J chain, which is required for polymeric Ig receptor-mediated IgA transport. J chain knockout mice were readily protected by heterosubtypic immunity, indicating that polymeric Ig receptor-mediated transport is not required. Better understanding of heterosubtypic immunity should be valuable in analyzing new vaccines, including peptide and DNA vaccines, intended to induce broadly cross-reactive immunity.

Mechanisms of heterosubtypic immunity to lethal influenza A virus infection in fully immunocompetent, T cell-depleted, beta2-microglobulin-deficient, and J chain-deficient mice

Immunity that is cross-protective between different influenza A virus subtypes (termed heterosubtypic immunity) can be demonstrated readily in some animals but only rarely in humans. Induction of heterosubtypic immunity in humans by vaccines would provide public health benefit, perhaps offering some protection against pandemics or other new influenza A strains. Therefore, we studied mechanisms mediating heterosubtypic immunity in mice. Immunization with either A/H1N1 or A/H3N2 virus protected mice against mortality following heterosubtypic challenge while providing modest reductions in lung virus titers. No cross-protection was seen with distantly related type B influenza virus. Depletion of CD4+ or CD8+ T cells or both around the time of challenge had no significant effect on survival, indicating that these cells are not required at the effector stage. beta2-microglobulin knockout mice could be protected readily against heterosubtypic challenge, confirming that class I-restricted T cells are not required. In beta2-microglobulin -/- mice, depletion of CD4+ T cells partially abrogated heterosubtypic immunity, showing that they play a role in these mice. Passive transfer of Abs to naive recipients protected against subsequent challenge with homologous but not heterosubtypic virus. Because a role for secretory Abs has been suggested, we studied dependence on the J chain, which is required for polymeric Ig receptor-mediated IgA transport. J chain knockout mice were readily protected by heterosubtypic immunity, indicating that polymeric Ig receptor-mediated transport is not required. Better understanding of heterosubtypic immunity should be valuable in analyzing new vaccines, including peptide and DNA vaccines, intended to induce broadly cross-reactive immunity.