Mice bearing the ob/ob mutation have impaired immunity

Rodent models of diabetic cardiomyopathy

Diabetic cardiomyopathy increases the risk of heart failure in individuals with diabetes, independently of co-existing coronary artery disease and hypertension. The underlying mechanisms for this cardiac complication are incompletely understood. Research on rodent models of type 1 and type 2 diabetes, and the use of genetic engineering techniques in mice, have greatly advanced our understanding of the molecular mechanisms responsible for human diabetic cardiomyopathy. The adaptation of experimental techniques for the investigation of cardiac physiology in mice now allows comprehensive characterization of these models. The focus of the present review will be to discuss selected rodent models that have proven to be useful in studying the underlying mechanisms of human diabetic cardiomyopathy, and to provide an overview of the characteristics of these models for the growing number of investigators who seek to understand the pathology of diabetes-related heart disease.

Impaired contact hypersensitivity in diet-induced obese mice

BACKGROUND

Epidemiological studies suggest that obesity is associated with the impairment of immunity. However, there is no experimental evidence that obesity prejudices immune responses.

OBJECTIVE

This study was designed to determine the effects of obesity on contact hypersensitivity (CHS) response using a diet-induced obese (DIO) mouse model.

METHODS

The effect of high fat diet (HFD) on CHS response to trinitrochlorobenzene (TNCB) was assessed by ear swelling, cytokine production, functional analysis of epidermal Langerhans cells, and adoptive transfer of immune cells. Immune response to ovalbumin was also analyzed in DIO mice.

RESULTS

C57BL/6 mice but not BALB/c mice that fed with HFD for 4 weeks or more became obese and showed impaired CHS response, although both strain of mice showed enhanced irritant response to TNCB. CHS response was slightly impaired when C57BL/6 mice fed with HFD for 1 or 2 weeks. This suggests that diet-induced obesity or the HFD itself impairs the CHS response in the susceptible mice. The adoptive transfer of immune cells from DIO mice sensitized with TNCB to naïve mice failed to show vigorous CHS, which suggests dysfunction of an afferent phase of CHS in DIO mice. However, the number and allo-stimulating ability of epidermal Langerhans cells were comparable between DIO mice and lean mice. In addition, the immune response to ovalbumin (delayed type hypersensitivity, and antigen-dependent production of antibodies and cytokine) was preserved in DIO mice.

CONCLUSION

These results suggest that the diet-induced obesity or the HFD only partially impairs immunity in the susceptible mice.

Leptin, malnutrition, and immune response in rural Gambian children

BACKGROUND

The adipocyte derived hormone, leptin, has cytokine like function and may mediate the effects of starvation on immunity. Mice with congenital leptin deficiency (ob/ob) have small hypocellular thymuses and impaired cellular immunity. In humans leptin influences the differentiation of naïve and memory cells in vitro, and genetic leptin deficiency has been associated with an ill defined susceptibility to infection.

AIMS

To describe the in vivo relation of leptin and immune function in children.

METHODS

Fasting plasma leptin concentrations, immune function (T and B cell mediated vaccine responses and delayed type hypersensitivity), and mucosal function (dual sugar permeability test and salivary sIgA concentrations) were measured in a cohort of 472 moderately undernourished rural Gambian children.

RESULTS

Leptin concentrations correlated with body fat assessed by mid upper arm circumference or BMI for age Z scores, and were very low compared to well nourished European norms (males 1.8 v 11.1 ng/ml; females 2.4 v 13.8 ng/ml). No detectable relations were found between leptin concentrations and any of the measures of immune or mucosal function.

CONCLUSIONS

The data confirm that leptin acts as a peripheral signal of energy restriction, but do not support an association between fasting plasma leptin levels and immune function in children of this age.

Cilia-associated respiratory (CAR) bacillus infection of obese mice

Cilia-associated respiratory (CAR) bacillus was identified in respiratory tract lesions of obese mice dying of chronic respiratory disease. Neither Mycoplasma pulmonis nor pathogenic bacteria were isolated from cultures of the lesions at necropsy, but there was serologic and histologic evidence of respiratory virus infection. Cranial-ventral areas of lung were firm and demarcated from unaffected lung at gross examination, and representative tissue sank in water. Microscopically, there was suppurative bronchopneumonia with extensive peribronchiole lymphocyte and plasma cell proliferation. The affected bronchiole epithelium was covered with a sheet of slightly basophilic, filamentous, gram negative bacteria. Bronchioles with lesser amounts of lymphocyte accumulations contained lesser amounts of filamentous bacteria. Bronchioles without filamentous bacteria lining the respiratory epithelium lacked peribronchiole lymphocyte accumulations. There was a high correlation between CAR bacillus-positive serology and the identification of diagnostic histologic lesions. CAR bacillus was readily stained using immunohistochemical methods, and the ultrastructural features were similar to that described in rat infections.

Enhanced tumor resistance and immunocompetence in obese (ob/ob) mice

Genetically obese mice (C57BL6/J-ob/ob) have enhanced resistance to metastasis of the B16 melanoma in comparison with lean littermate controls. Here we show that this difference is not due to differences in the health status of these mice. We show also that the obese mice have enhanced immunocompetence as indicated by enhanced proliferative responses of their splenic lymphocytes to T-cell mitogens but not to a B-cell mitogen. The obese mice also produced twice as many antibody-secreting cells in their spleens in response to immunization in vivo with sheep erythrocytes as did lean mice. There were no differences between the two genotypes in cytolytic T lymphocyte activity after immunization in vivo with allogeneic cells. An opioid theory of enhanced immunocompetence could account for our results.

Inhibition of lymphocyte capping by fatty acids in mouse and man

Lipid-enriched diets have been related to a high cancer incidence in experimental animals for many years, and more recently, to assorted defects on the immune response. We investigated the effect of incubating human or murine (C3H/HEJ) lymphocytes with saturated (16:0) and unsaturated (18:1, 18:2, 18:3, 20:4) fatty acids (12 micrograms for each 10(7) cells), on the ability to cap with antihuman or antimouse anti-IgM, mu-chain specific antibody. Capping was also tested in obese (ob/ob, C57BL/6J) mice. Capping at 30 and 60 min was reduced by fatty acid incubation to 10-30% of control values in humans (p less than .001), and to 30% of control values in mice (p less than .01), regardless of degree of unsaturation. ob/ob capped normally. A lymphocyte membrane effect caused by fatty acids is observed in these experiments. Whether this is related to the dysimmunity caused by lipid diets cannot be assessed from our data, especially since all fatty acids, regardless of unsaturation, reduced the capping phenomenon.

Mutations in mice that influence natural killer (NK) cell activity

A series of mutations in mice was tested for splenic NK-cell activity against YAC-1 target cells. Mutations at six loci that reduce NK-cell activity in the homozygous state were identified, including beige (bg), hairless (hr), motheaten (me), obese (ob), steel (Sl) and, to lesser extent, dominant spotting (W). Motheaten mice displayed the most profound NK-cell deficiency, with NK-cell activity virtually absent. Two mutations, nude (nu) and lymphoproliferation (lpr), produced elevated NK-cell-mediated lysis. The double homozygous recessive nu/nu bg/bg nude-beige mouse was viable and NK-cell-deficient, with activity slightly higher than that of +/? bg/bg beige littermate controls. Pigmentation mutants related to beige, including pale ears (ep), pearl (pe) and ruby eyes (ru2J) did not dramatically influence NK-cell levels. Unlike the obese gene, other mutations leading to obesity, diabetes (db) and yellow (Ay), did not impair NK-cell function. The possible site of gene action of these mutations in the NK-cell pathway is discussed.