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ABSTRACTCryptosporidium parvuminfection of T-cell receptor alpha (TCR-α)-deficient mice results in a persistent infection. In this study, treatment with a polyamine analogue (SL-11047) preventedC. parvuminfection in suckling TCR-α-deficient mice and cleared an existing infection in older mice. Treatment with putrescine, while capable of preventing infection, did not clear C. parvumfrom previously infected mice. These findings provide further evidence that polyamine metabolic pathways are targets for new anticryptosporidial chemotherapeutic agents.

Cryptosporidium parvum infection of T-cell receptor alpha (TCR-alpha)-deficient mice results in a persistent infection. In this study, treatment with a polyamine analogue (SL-11047) prevented C. parvum infection in suckling TCR-alpha-deficient mice and cleared an existing infection in older mice. Treatment with putrescine, while capable of preventing infection, did not clear C. parvum from previously infected mice. These findings provide further evidence that polyamine metabolic pathways are targets for new anticryptosporidial chemotherapeutic agents.

ABSTRACTMycobacterium aviumsubsp. paratuberculosisinfection of cattle results in a chronic granulomatous enteritis. Clinical disease (i.e., cachexia, diarrhea, and high fecal bacterial counts) is preceded by a lengthy subclinical stage of disease. The immunologic mechanisms associated with the progression of infected cattle from subclinical to clinical disease are unclear. In this study, a cell proliferation assay was used in combination with flow cytometry to compare peripheral blood lymphocyte responses of cattle with subclinical paratuberculosis to responses of cattle with clinical paratuberculosis. B cells from cattle with subclinical disease proliferated vigorously upon stimulation with M. aviumsubsp. paratuberculosisantigen, with up to 12.4% of the total B cells responding. However, B cells from cattle with clinical disease did not proliferate upon antigen stimulation despite good proliferation in response to concanavalin A stimulation. In addition, these animals had high percentages of peripheral blood B cells. B cells from noninfected animals did not proliferate upon M. aviumsubsp. paratuberculosisantigen stimulation. Thus, it appears that B-cell proliferation is a sensitive indicator of subclinical Johne’s disease. Furthermore, the immunologic mechanisms responsible for the antigen-specific unresponsiveness of peripheral blood B cells may be significant in the eventual progression from subclinical to clinical Johne’s disease in cattle.

In vascular smooth muscle cells, the induction of early growth response genes involves the Janus kinase (JAK)/signal transducer and activators of transcription (STAT) and the Ras/Raf-1/mitogen-activated protein kinase cascades. In the present study, we found that electroporation of antibodies against MEK1 or ERK1 abolished vascular smooth muscle cell proliferation in response to either platelet-derived growth factor or angiotensin II. However, anti-STAT1 or -STAT3 antibody electroporation abolished proliferative responses only to angiotensin II and not to platelet-derived growth factor. AG-490, a specific inhibitor of the JAK2 tyrosine kinase, prevented proliferation of vascular smooth muscle cells, complex formation between JAK2 and Raf-1, the tyrosine phosphorylation of Raf-1, and the activation of ERK1 in response to either angiotensin II or platelet-derived growth factor. However, AG-490 had no effect on angiotensin II- or platelet-derived growth factor-induced Ras/Raf-1 complex formation. Our results indicate that: 1) STAT proteins play an essential role in angiotensin II-induced vascular smooth muscle cell proliferation, 2) JAK2 plays an essential role in the tyrosine phosphorylation of Raf-1, and 3) convergent mitogenic signaling cascades involving the cytosolic kinases JAK2, MEK1, and ERK1 mediate vascular smooth muscle cell proliferation in response to both growth factor and G protein-coupled receptors.

The susceptibilities of passively immunized principal and nonimmunized control suckling mice to orogastric challenge with Cryptosporidium parvum oocysts were compared. Principals were suckled by dams that had recovered from C. parvum infection. Controls were suckled by dams reared free of C. parvum infection. Principals and controls were equally susceptible to challenge. Principals were susceptible even when their dams were hyperimmunized by oral and parenteral booster inoculations with C. parvum oocysts. Immune dams produced serum antibody against C. parvum, while nonimmune dams did not. Anti-cryptosporidia immunoglobulin G (IgG) and IgA were demonstrated in whey extracted from the stomachs of principals that had suckled immune dams but not in whey extracted from the stomachs of controls. It was concluded that passive lacteal immunity is not an efficient means of protection against cryptosporidiosis in mice. As in other coccidian infections, protective immunity against cryptosporidiosis may depend more on immune cells than on antibody.

Adult mice are more resistant than neonatal mice to intestinal colonization with the protozoan parasite Cryptosporidium parvum. Development of a mature intestinal flora may play a role in this resistance. We compared susceptibilities to colonization with C. parvum in adult conventional mice, adult germfree mice, and adult conventional mice treated with oral antibiotics to deplete the intestinal flora. Germfree mice of both CD1 and BALB/c strains were colonized at day 7 following inoculation with C. parvum oocysts isolated from the feces of an infected, diarrheic calf. Age-matched conventional mice of the same strains were comparatively resistant to colonization. Conventional mice treated with antibiotics remained resistant to colonization. These results suggest that the microflora in the intestine was not the sole determinant of resistance or susceptibility to colonization. The germfree adult mouse as an experimental model of cryptosporidiosis is discussed.

An early event in signaling by the G-protein-coupled angiotensin II (Ang II) AT1 receptor in vascular smooth muscle cells is the tyrosine phosphorylation and activation of phospholipase Cgamma1 (PLCgamma1). In the present study, we show that stimulation of this event by Ang II in vascular smooth muscle cells is accompanied by binding of PLCgamma1 to the AT1 receptor in an Ang II- and tyrosine phophorylation-dependent manner. The PLCgamma1-AT1 receptor interaction appears to depend on phosphorylation of tyrosine 319 in a YIPP motif in the C-terminal intracellular domain of the AT1 receptor and binding of the phosphorylated receptor by the most C-terminal of two Src homology 2 domains in PLCgamma1. PLCgamma1 thus binds to the same site in the receptor previously identified for binding by the SHP-2 phosphotyrosine phosphatase.JAK2 tyrosine kinase complex. A single site in the C-terminal tail of the AT1 receptor can, therefore, be bound in a ligand-dependent manner by two different downstream effector proteins. These data demonstrate that G-protein-coupled receptors can physically associate with intracellular proteins other than G proteins, creating membrane-delimited signal transduction complexes similar to those observed for classic growth factor receptors.