The nature of immunosuppression in Trypanosoma brucei infections in mice: I. The role of the macrophage

The functional integrity of the mononuclear phagocytic system (MPS) in mice infected with Trypanosoma brucei was investigated with regard to its possible significance in the aetiology of the immunosuppression characteristic of this disease.

In infected mice the spleens and lymph nodes were grossly enlarged, and on histological examination it was shown that the MPS of the liver, lymph nodes, spleen and bone marrow was markedly expanded. Macrophages presented an active appearance and often contained cellular debris. Clearance of intravenously injected sheep red blood cells (SRBC) was increased, in that 1 hour after injection, 2–6 times more ⁵¹Cr-labelled SRBC had disappeared from the circulation of infected, compared to uninfected mice; this was due largely to an increased uptake by the expanded phagocytic system of the liver.

The intrinsic immunogenic potential of individual macrophages appeared to be unimpaired as judged by the ability of SRBC-containing macrophages from infected mice to elicit a response in syngeneic normal recipient mice.

It was concluded that the only evidence that immunosuppression might be associated with an altered activity of the MPS was an increased hepatic uptake of particulate antigen with a relative failure of splenic uptake. Together these might be responsible for a reduction in the concentration of antigen in the tissues of an enlarged spleen below the level necessary to initiate the formation of antibody.

     

The specificity of the anti-haemagglutinin antibody response induced in man by inactivated influenza vaccines and by natural infection.

The anti-haemagglutinin antibody response in adult human volunteers to inactivated whole virus or tween ether split influenza A/Victoria/75 (H3N2) and A/Scotland/74 (H3N2) virus vaccines was investigated using antibody absorption and single-radial-haemolysis (SRH) techniques. The concentrations of haemagglutinin (HA), nucleoprotein (NP) and matrix (M) antigens measured by single radial diffusion (SRD) and rocket immunoelectrophoresis were similar for both the whole virus and split vaccines. Whole virus and split vaccines induced crossreactive (CR) antibody in 87% of vaccinees. Strain specific (SS) antibody to A/Hong Kong/1/68 of the homologous virus was induced less frequently than CR antibody. Higher anti-haemagglutinin antibody titres were detected in persons receiving the split virus vaccines than in those receiving the whole virus vaccines. No antibody to the type-specific matrix protein was detectable, but 33% of volunteers developed an antibody rise to type-specific nucleoprotein antigen. The specificity of the anti-haemagglutinin antibody response in human adults to natural infection with A/Port Chalmers/73 (H3N2) virus was similar to that induced by inactivated vaccines in that a high proportion of subjects developed CR anti-haemagglutinin antibody, which reacted with A/Hong Kong/68 virus and the homologous A/Port Chalmers/73 virus, and SS antibody for A/Hong Kong/68 virus but SS antibody for A/Port Chalmers/73 virus was infrequently stimulated by natural infection.     

5-Fluorocytosine Resistance in Cryptococcus neoformans

Isolates of Cryptococcus neoformans from six patients were obtained before and after unsuccessful therapy with 5-fluorocytosine (5-FC). Post-therapy isolates exhibited massive and stable 5-FC resistance. The frequency of drug-resistant mutants in susceptible isolates of C. neoformans was <0.001% (70.4 +/- 17.9 per 10(7) cryptococci), whereas mutant frequencies in resistant isolates approached 100%. Non-drug-induced, spontaneously appearing 5-FC resistant mutants were documented in four susceptible isolates of C. neoformans by use of the statistical method of fluctuation analysis. Mutation rates on these same four isolates ranged from 1.2 x 10(-7) to 4.8 x 10(-7). Total intracellular uptake and incorporation of cytosine-5-(3)H (CyH(3)) and 5-fluorocytosine-2-(14)C (5-FC(14)) into a trichloroacetic acid-insoluble fraction were markedly reduced in six isolates with in vivo-acquired resistance when compared with susceptible pretreatment strains from the same patients. Five of these six isolates also had acquired massive resistance to 5-fluorouracil (5-FU), suggesting that a mutation in the uridine-5'-monophosphate pyrophosphorylase was responsible for drug resistance. The sixth isolate, which remained susceptible to 5-FU, appeared to have a defect in a cytosine-specific permease accounting for 5-FC resistance. A single isolate with in vitro-acquired 5-FC and 5-FU resistance had no reduction in uptake or incorporation of CyH(3) or 5-FC(14). The mechanism of resistance in this isolate is discussed.     

The possible use ofTrypanosoma musculi infection in mice as a screening test for potentialTrypanosoma cruzi-active drugs

The ability of a range of trypanocidal drugs, including a number known to be active inTrypanosoma cruzi infections were tested againstTrypanosoma musculi infections in the mouse. The ability of these drugs, particularly in their ability to eliminate the cryptic phase ofT. musculi infections remaining in the kidneys, was investigated and their activity against this phase ofT. musculi largely paralleled their known activity againstT. cruzi infections. It is suggested that this could be used as a preliminary screening test for potentialT. cruzi-active drugs.     

Paclitaxel induces the phosphorylation of the eukaryotic translation initiation factor 4E-binding protein 1 through a Cdk1-dependent mechanism

Initial chemotherapeutic treatment triggers a stress-related response, which can lead to an increase in the expression of survival proteins. In this study we examine whether paclitaxel (PTX) alters the expression and/or phosphorylation of the translation initiation proteins, eukaryotic initiation factor 4E (eIF-4E) and 4E-binding protein (4E-BP1), a suppressor of eIF-4E in the dephosphorylated state. We found that PTX induced the hyperphosphorylation of 4E-BP1 in the breast cancer cell line, MDA MB 231, which reduced its association with eIF-4E, but did not alter the expression and phosphorylation of eIF-4E. The hyperphosphorylation of 4E-BP1 correlated with G2/M accumulation and with an increase in the phosphorylation of cdk1 substrates. Cotreatment with a histone deacetylase inhibitor (an indirect inhibitor of cdk activity), purvalanol A and roscovitine (direct cdk inhibitors), and the reduction of cyclin B expression using RNA interference decreased the hyperphosphorylation of 4E-BP1 in PTX treated cells. The hyperphosphorylation of 4E-BP1 by PTX increased the association of eIF-4E with eIF-4G, whereas cotreatment with purvalanol A inhibited the association of eIF-4E with eIF-4G in PTX treated cells. Taken together, our data suggest that PTX-increases the functional level of eIF-4E by promoting the hyperphosphorylation and release of 4E-BP1 through a cdk1-dependent mechanism.