Spontaneous lytic activity against heterologous erythrocytes in cotton rat (Sigmodon hispidus) serum.

Although innate immunity has been well studied in laboratory animal models, no such documentation exists for wild species possessing a diversity of physiological adaptations to their environment. We examined the blood sera of 188 hispid cotton rats (Sigmodon hispidus) for naturally occurring hemolytic activity against heterologous erythrocytes. Ninety-two percent of the blood sera samples from cotton rats lysed sheep erythrocytes. All sera tested against chicken erythrocytes showed hemolytic activity, while only 44% of the same sera could lyse bovine erythrocytes. No hemolytic activity was present in cotton rat sera against erythrocytes from other rodent species (Eastern woodrat, Neotoma floridana, and pine vole, Microtus pinetorum). Hemolytic activity was heat labile and appeared to be mediated through the classical complement pathway. The protective nature of this hemolytic factor is unclear but it is probably directed at a more relevant molecule. These data, along with other reports of naturally occurring target specific serum factors in the cotton rat, may reflect the importance of innate protective mechanisms to small mammal populations.

Cellular immune responses of nutritionally stressed juvenile cotton rats (Sigmodon hispidus) during acute benzene exposure.

Wild juvenile cotton rats (Sigmodon hispidus) were used in this study to examine the effects of exposure to cyclophosphamide (CY) or differing levels of benzene on selected measures of cellular immunity following dietary protein restriction. Benzene caused marginal immunotoxicity as indicated by suppressed splenocyte proliferation and total circulating neutrophils. Cyclophosphamide and also crude protein restriction induced severe immune lesions manifested as thymus and spleen atrophy, depressed delayed hypersensitivity response, reduced proliferative capacity of splenocytes, and reduced numbers of total leukocytes, lymphocytes, and splenocytes. Although severe immune modulation resulted from the individual effects of CY exposure and dietary protein restriction, there was little statistically significant toxicant-diet interaction.

Selected immune responses of adult cotton rats (Sigmodon hispidus) to dietary restriction.

1. We examined the influence of moderate to severe dietary restriction on immune system function in adult cotton rats. Animals (N = 80) were fed ad lib. (controls) or restricted [moderate = 80% ad lib. for 1 or 2 weeks; severe = 80% ad lib. for 1 or 2 weeks followed by 40% ad lib. for one (week 3) or two (week 4) additional weeks] amounts of food for 1-4 weeks. 2. Average body weight loss for severely restricted animals in week 4 was 17%; dietary treatments had no measurable effect on hematological parameters (hematocrit, white blood cell count), lymphoid organ weights (thymus gland, spleen, popliteal lymph nodes), and mononuclear cell yields from lymphoid organs. 3. Cell-mediated immune function was assessed in vitro by a lymphoproliferative response assay and in vivo by a delayed-type hypersensitivity response assay. 4. Proliferative responses of spleen cell cultures stimulated with concanavalin A (Con A, Canavalia ensiformis) and pokeweed (PWM, Phytolacca americana) were normal or significantly greater among moderately restricted than control cotton rats during week 1 and week 2. 5. Lymphoproliferative responses of severely restricted animals were normal or reduced during week 3 and week 4. 6. Delayed-type hypersensitivity responses to the contact antigen oxazolone were significantly depressed among severely restricted animals in week 4 compared to controls. 7. In comparison with laboratory rodent strains, our initial results indicate that immune system function in adult cotton rats is not as sensitive to short term (1-4 weeks) periods of dietary restriction. 8. Immune system function was related to changes in body weight as a result of feed restriction.

Gut associated lymphoid tissue in the cotton rat (Sigmodon hispidus) and its response to protein restriction.

We examined age and nutritional related changes in the distribution and size of gut associated lymphoid tissues in the intestinal tract of cotton rats (Sigmodon hispidus). Peyer's patches in the small intestine are prominent, ranging from four to 13, and increase in size (surface area) with age. The average Peyer's patch in the adult cotton rat measured 23.9 mm2. Lymphoid tissue in the cecum was primarily limited to a large aggregate located in the vermiform appendix, which increased in size with age. Age related changes in the number of visible lymphoid follicles in the large intestine were highly significant, increasing from 24.8 in juveniles to 45.1 in adults. Weights of dissectable Peyer's patch tissue in animals consuming a low protein diet were significantly lower in juveniles and greater in subadults compared to those on high protein diets. Relative weights of Peyer's patch tissue averaged 84 to 95% more in low protein-fed animals than in the group on the high quality protein diet. Our results suggest that peripheral lymphoid tissues in wild cotton rats are more resistant to protein deficiencies than other tissues in the body and could be a useful index for assessing nutritional status.

Primary immune responses of selected small mammal species to heterologous erythrocytes.

1. We surveyed the primary humoral immune responsiveness of six small mammal species (Peromyscus leucopus, Microtus pinetorum, Perognathus hispidus, Neotoma floridana, Onychomys leucogaster, Mus musculus) collected from wild populations in central Oklahoma using sheep red blood cells (SRBC) as the immunogen and a splenic plaque-forming cell (PFC) assay. 2. Individuals within each wild species examined produced antibodies to a single intraperitoneal injection of SRBC, however, considerable interspecific and intraspecific variation in responsiveness was indicated. 3. Overall, primary immune responsiveness varied from 0 to 5013 PFC/10(6) cells. Spleen weights, total splenic nucleated cell yields, PFC/spleen, PFC/mg spleen, and PFC/10(6) cells were significantly different among species. 4. Mean cell yield in M. pinetorum was greater than in P. leucopus and CD-1 laboratory mice (included as positive controls). Number of PFC/10(6) cells was greater in CD-1 laboratory mice than P. hispidus and P. leucopus. The coefficient of variation for PFC/10(6) cells in CD-1 laboratory mice was 38% compared to 109, 129, and 56% for M. pinetorum, P. hispidus, and P. leucopus, respectively. 5. Interspecific and intraspecific differences among wild species may be a reflection of disparate life histories and other environmental selection pressures.