RetroDISCO: Clearing technique to improve quantification of retrograde labeled motor neurons of intact mouse spinal cords

BACKGROUND

Quantification of the number of axons reinnervating a target organ is often used to assess regeneration after peripheral nerve repair, but because of axonal branching, this method can overestimate the number of motor neurons regenerating across an injury. Current methods to count the number of regenerated motor neurons include retrograde labeling followed by cryosectioning and counting labeled motor neuron cell bodies, however, the process of sectioning introduces error from potential double counting of cells in adjacent sections.

NEW METHOD

We describe a method, retroDISCO, that optically clears whole mouse spinal cord without loss of fluorescent signal to allow imaging of retrograde labeled motor neurons using confocal microscopy.

RESULTS

Complete optical clearing of spinal cords takes four hours and confocal microscopy can obtain z-stacks of labeled motor neuron pools within 3-5min. The technique is able to detect anticipated differences in motor neuron number after cross-suture and conduit repair compared to intact mice and is highly repeatable.

COMPARISON WITH EXISTING METHOD

RetroDISCO is inexpensive, simple, robust and uses commonly available microscopy techniques to determine the number of motor neurons extending axons across an injury site, avoiding the need for labor-intensive cryosectioning and potential double counting of motor neuron cell bodies in adjacent sections.

CONCLUSIONS

RetroDISCO allows rapid quantification of the degree of reinnervation without the confounding produced by axonal sprouting.

Antibody-dependent killing of virus-infected targets by NK-like cells in bovine blood

Natural killer (NK) cell lysis of target cells by an Fc receptor-mediated mechanism has not been conclusively demonstrated in cattle (Campos and Rossi, Vet. Immunol. Immunopathol. 8, 351-362, 1985), although it is well recognized in other species (Sulica et al., Nat. Immun. 14, 123-133, 1995). To resolve this problem, bovine peripheral blood mononuclear cells were completely depleted of adherent monocyte/macrophage type cells. The resulting enriched population of lymphocytes, was totally devoid of adherent monocytes, but contained up to 2% NK-like cells. On their own, this population had very low background levels of cytotoxicity for virus-infected target cells in 51chromium release assays, but following the addition of virus-specific antibodies, high levels of lysis were observed. This enhanced level of antibody-dependent cytotoxicity demonstrated that bovine NK-like cells can mediate killing of targets by an Fc receptor-mediated mechanism as has been demonstrated for NK cells from other species.

Effect of parainfluenza-3 virus challenge on cell-mediated immune function in parainfluenza-3 vaccinated and non-vaccinated calves

A group of four conventional, colostrum-fed calves was vaccinated with live parainfluenza type 3 (PI-3) virus vaccine at 1 and 5 weeks of age. A group of four control calves was treated with cell culture medium at the same time. Two weeks after the second vaccination, both groups of calves were challenged with PI-3 virus by a combined respiratory route. Blood and nasal mucus samples were collected at intervals, and alveolar macrophages were recovered before and after challenge by bronchoalveolar lavage. The results demonstrated that clearance of virus, as indicated by presence of virus antigen was more rapid in previously vaccinated calves. Several alveolar macrophage functions were markedly reduced in all calves 5 to 7 days following virus challenge, although microbicidal activity was unaffected, compared to the controls. The production of neutrophil chemotactic factors by alveolar macrophages occurred more rapidly after virus challenge in the previously vaccinated calves and this correlated with a more rapid neutrophil influx into the lungs in these animals.

Studies on the efficacy of intranasal vaccination for the prevention of experimentally induced parainfluenza type 3 virus pneumonia in calves

The efficacy of intranasal vaccination in preventing or limiting disease of the lower respiratory tract induced by parainfluenza 3 (PI3) virus was evaluated under experimental conditions, using a commercially available live vaccine containing a temperature-sensitive strain of PI3 virus. In a preliminary study four colostrum-deprived calves were vaccinated intranasally at one week and again at two months of age, and two similar calves were given an intranasal placebo. After the second vaccination serum antibodies to PI3 virus were detected in all four vaccinated calves, but not in the control animals. Seventeen days after the second vaccination all six calves were challenged with virulent PI3 virus, and they were killed six days later. The clinical scores and the extent of pulmonary consolidation were reduced in the vaccinated animals; PI3 virus was detected in the upper and lower respiratory tract of the control calves but in none of the vaccinated calves. In a larger scale study with 14 colostrum-fed calves, seven were vaccinated at one week and again at five weeks of age, and seven were given an intranasal placebo. Two weeks after the second vaccination all 14 calves were challenged with virulent PI3 virus. The clinical scores and lung consolidation were significantly reduced in the vaccinated calves in comparison with the controls. Six days after infection, 10 of the 14 calves were killed; PI3 virus was detectable in the nasal secretions of all seven control calves but in only one of the vaccinated animals, and PI3 viral antigen was detected in the lungs of the control calves but not in those of the vaccinated animals. One of the vaccinated calves had developed a severe clinical response after the challenge, but it had only minor lung consolidation when killed.

Cytotoxic interactions between bovine parainfluenza type 3 virus and bovine alveolar macrophages

This paper describes an investigation of the cytotoxic activity of bovine alveolar macrophages for parainfluenza type 3 (PI-3) virus-infected target cells, using 51Cr release assays. Alveolar macrophages from uninfected calves were shown to be capable of killing PI-3 virus infected cells without the presence of antibody or complement (antibody-independent cell-mediated cytotoxicity). The level of killing was shown to vary from animal to animal with specific lysis values ranging from <5% to 70%. Presence of PI-3 virus antiserum was shown to inhibit, rather than enhance macrophage cytotoxicity in a dose-dependent manner, suggesting that bovine alveolar macrophages do not always exhibit antibody-dependent lysis in all cases. Following intranasal and intratracheal inoculation of calves with PI-3 virus, the level of cytotoxicity by macrophages lavaged from the lungs of the calves increased substantially, and by Day 5 post inoculation, levels of 95% to 98% specific lysis were recorded. After Day 5, the killing ability decreased rapidly to low levels. Cell-free lavage fluids, collected from PI-3 virus infected and control calves at various times throughout the experiment, were incubated with aliquots of an alveolar macrophage population from an uninfected donor calf, which initially showed a low level of killing, and were subsequently added to PI-3 virus infected target cells. The recorded levels of cytotoxicity, mirrored those which were seen with the initial macrophage effector cells from the infected and control animals, suggesting that macrophage cytotoxicity was largely controlled by extracellular factors.

Cytotoxicity of bovine leucocytes for parainfluenza type-3 virus-infected cells

The cytotoxic effect of bovine neutrophils, alveolar macrophages, monocytes and lymphocytes for parainfluenza type-3 (PI-3) virus-infected cells in 51chromium-release assays is described. Specific lysis of virus-infected target cells with PI-3 virus antibody and complement was first observed 8 h after infection coincident with the appearance of haemadsorption-positive cells. Specific lysis increased rapidly reaching a peak 18-24 h after infection. This increase was paralleled by the increase in the percentage of cells with surface haemagglutinin. Target cells were subsequently used in 51chromium-release assays between 18 and 20 h after virus infection. Antibody-independent killing of PI-3 virus-infected cells was observed with neutrophils, alveolar macrophages and lymphocytes. Levels of specific lysis up to 30% for neutrophils and 68% for alveolar macrophages were observed, although there was considerable variation in activity from animal to animal. Lymphocyte preparations showed levels of cytotoxicity up to 20% in some cases while monocytes had low killing ability. Addition of PI-3 virus-specific antibodies enhanced killing by neutrophils, monocytes and lymphocytes but inhibited killing by alveolar macrophages. Complement, particularly guinea pig complement, was cytotoxic for virus-infected but not for uninfected cells, and also considerably enhanced the cytotoxic effect of neutrophils and lymphocytes.

Effect of macrophages and in vitro infection with parainfluenza type 3 and respiratory syncytial viruses on the mitogenic response of bovine lymphocytes

Bovine blood lymphocytes, depleted of macrophages by absorption on plasma-gelatin coated plastic flasks, followed by passage through Sephadex G-10 columns, failed to respond to pokeweed mitogen stimulation. Adherent monocytes or alveolar macrophages added to purified lymphocyte preparations at 10% or less were able to restore the transformation response. Exposure of alveolar macrophages or purified lymphocytes to 2 bovine respiratory syncytial virus strains for 24 hours substantially reduced the transformation response when mixed with uninfected lymphocytes or macrophages. Exposure of alveolar macrophages or purified lymphocytes to 2 bovine parainfluenza type 3 virus strains produced a similar reduction in activity after 48 hours. Heat inactivation of the viruses removed their inhibitory ability. Immunofluorescence studies revealed that both alveolar macrophages and lymphocytes were permissive for parainfluenza type 3 virus, whereas only a small number of alveolar macrophages and lymphocytes were infected with respiratory syncytial virus. The results suggest that both viruses are capable of adversely affecting the interaction between macrophages and lymphocytes, although the mechanisms by which this is achieved may be different.