Prioritisation of areas for early detection of southward movement of arctic fox rabies based on historical surveillance data in Quebec, Canada.

Arctic rabies virus variant (ARVV) is enzootic in Quebec (Canada) north of the 55th parallel. With climate change, increased risk of re-incursion of ARVV in more densely populated southern regions raises public and animal health concerns. The objective of this study was to prioritise geographical areas to target for an early detection of ARVV incursion south of the 55th parallel based on the historical spatio-temporal trends of reported rabies in foxes in Quebec. Descriptive analyses of fox rabies cases from 1953 to 2017 were conducted. Three periods show increases in the number of fox rabies cases in southern regions and indicate incursion from northern areas or neighbouring provinces. The available data, particularly in central and northern regions of the province, were scarce and of low spatial resolution, making it impossible to identify the path of spread with precision. Hence, we investigated the use of multiple criteria, such as historical rabies cases, human population density and red fox (Vulpes vulpes) relative abundance, to prioritise areas for enhanced surveillance. This study underscores the need to define and maintain new criteria for selecting samples to be analysed in order to detect rapidly ARVV cases outside the current enzootic area and any potential re-incursion of the virus into central and southern regions of the province.

Rabies control in North America - past, present and future.

In the first half of the 20th century, rabies in dogs affected Canada, Mexico and the United States of America (USA). However, the role of wildlife in the transmission of the rabies virus was also recognised and outbreaks affecting both wildlife and domestic animals were documented. Canine rabies has since been eliminated from Canada and the USA, and is now only found sporadically in a few southern states of Mexico. Wildlife variant rabies viruses, found throughout the continent and geographically associated with specific reservoir species, have notable public and animal health, as well as economic, impacts. Early rabies control efforts included legislated dog management strategies and wildlife population reduction, which met with varying success. In the last 30 years, programmes for the control of rabies in dogs and wildlife have benefited from an 'Integrated Management Approach', combining education, vaccination (parenteral and oral), strategic population control, responsible pet ownership and effective stewardship of natural resources, in addition to cooperation and collaboration among local, national and international stakeholders. Looking ahead, the goal of eliminating specific wildlife virus variants will be challenged by the potential range expansion of reservoir species, due to climate change and other factors, and the risk of re-introducing eliminated virus variants. To be successful, programmes must be sustained and accompanied by advances in vaccines, enhanced distribution strategies, monitoring in the field and effective modelling of disease spread. They should also be informed by robust case surveillance, phylogenetics and an increased knowledge of vector ecology.

Au Canada, au Mexique et aux États-Unis d'Amérique, la rage canine a sévi jusqu'au milieu du xxe siècle. Le rôle de la faune sauvage dans la transmission du virus de la rage y était également connu et des foyers affectant aussi bien des espèces sauvages que domestiques étaient observés et étudiés. Depuis, le Canada et les États-Unis ont réussi à éliminer la rage canine de leur territoire, de sorte que cette maladie ne se déclare plus que sous forme sporadique dans certains états du Sud du Mexique. En revanche, les variants des virus de la rage qui affectent la faune sauvage circulent sur tout le territoire continental, leur présence étant géographiquement associée à celle de certaines espèces déterminées qui font office de réservoirs, avec des conséquences importantes pour la santé tant publique qu'animale et pour l'économie. Les premières mesures de lutte appliquées contre la rage, essentiellement des stratégies de contrôle des populations de chiens à travers une législation appropriée et une réduction de certaines populations d'animaux sauvages, ont rencontré un succès variable. Depuis une trentaine d'années, les programmes de lutte contre la rage chez les chiens et les animaux sauvages font l'objet d'une « démarche de gestion intégrée ¼ associant des campagnes de sensibilisation, l'application de la vaccination (par voies parentérale et orale), la maîtrise stratégique des populations, la responsabilisation des propriétaires de chiens et la gestion efficace des ressources naturelles, en plus de la coopération et de la collaboration entre les parties prenantes à l'échelle locale, nationale et internationale. En ce qui concerne l'avenir, l'objectif d'éliminer les variants du virus affectant spécifiquement la faune sauvage se heurte à l'expansion potentielle du spectre d'espèces réservoirs à la faveur du changement climatique et d'autres facteurs, ainsi qu'au risque de réintroduction de variants du virus précédemment éliminés. Pour réussir, les programmes doivent être soutenus dans le temps et s'accompagner d'avancées en matière de vaccins, de stratégies de distribution renforcées, d'un meilleur suivi sur le terrain et d'une modélisation efficace de la propagation de la maladie. Ils doivent également reposer sur une surveillance robuste des cas, sur des données phylogénétiques et sur une connaissance accrue de l'écologie des vecteurs.

En la primera mitad del siglo XX, la rabia estaba presente en la población canina del Canadá, México y los Estados Unidos de América, aunque también se conocía la función de los animales silvestres en la transmisión del virus y se habían descrito brotes que afectaron a la vez a animales domésticos y silvestres. Posteriormente la rabia canina fue eliminada del Canadá y los EE.UU. mientras que en México, a día de hoy, solo hace apariciones esporádicas en unos pocos estados meridionales. Las variantes del virus rábico que afectan a la fauna silvestre, presentes en todo el continente y geográficamente ligadas a determinadas especies que actúan de reservorio, tienen notables repercusiones en la salud pública, la sanidad animal y la economía. Entre las primeras iniciativas de lucha contra la rabia había medidas de reducción de las poblaciones de animales silvestres y estrategias de gestión de la población canina impuestas por vía legislativa que se aplicaron con éxito variable. En los últimos 30 años, los programas de lucha antirrábica en perros y animales silvestres han incorporado métodos de «gestión integrada¼ que aúnan labores de pedagogía, vacunación (parenteral y oral), control estratégico de poblaciones, propiedad responsable de los animales de compañía y eficaz administración de los recursos naturales, además de la cooperación y colaboración entre los interlocutores locales, nacionales e internacionales. De cara al futuro, el objetivo de eliminar variantes víricas específicas de la fauna silvestre se verá comprometido por el posible crecimiento del área de distribución de las especies reservorio (debido al cambio climático y otros factores) y por el riesgo de reintroducción de variantes víricas eliminadas. Para que los programas tengan éxito deben ser duraderos y acompañarse de avances en las vacunas, mejores estrategias de distribución, tareas de seguimiento sobre el terreno y elaboración de modelos eficaces de diseminación de la enfermedad. También deben alimentarse de una sólida vigilancia de casos, estudios filogenéticos y un mejor conocimiento de la ecología de los vectores.

Raccoon rabies outbreak in Hamilton, Ontario: A progress report.

BACKGROUND: Raccoon rabies is caused by a variant of the rabies virus found in raccoons but transmissible to other mammalian species, including humans. The disease of rabies caused by raccoon variant rabies virus is indistinguishable from rabies caused by other rabies virus variants. OBJECTIVE: This paper describes the raccoon rabies outbreak in Ontario (identified in December 2015) and the control measures undertaken to curb the spread of the epizootic using the One Health approach. INVESTIGATION AND RESULTS: Representatives from local, provincial and federal agencies collectively activated a raccoon rabies response that involved policy updates, enhanced surveillance, a public education campaign and mass vaccination of wildlife and domestic animals. Between December 2015 and June 2017, 338 animals tested positive for raccoon rabies in Ontario. While the majority of the cases were raccoons, there was significant spillover into striped skunks, as well as other species including two cats, a fox and a llama. Viral genome sequencing determined that this epizootic was likely caused by long-distance translocation from the United States. CONCLUSION: This outbreak of raccoon rabies is by far the largest to have occurred in Canada and the first raccoon rabies outbreak documented in a densely populated urban area. This is also the first time this rabies virus variant has been identified in a domestic animal in Canada. A collaborative approach involving numerous stakeholders in the public and private sectors has been instrumental in addressing this epizootic. Though case incidence appears to be declining, several years will likely be required to reach elimination. Continued collaboration between these agencies is necessary to achieve this goal.

Oral vaccination and protection of striped skunks (Mephitis mephitis) against rabies using ONRAB®.

Skunks are one of the most important rabies vector species in North America due to their wide geographic distribution, high susceptibility to the rabies virus, and tendency to inhabit areas around human dwellings and domestic animals. Oral vaccination is a cost-effective, socially acceptable technique often used to control rabies in terrestrial wildlife; however, control of rabies in skunks has proven especially challenging due to the lack of a vaccine effective by the oral route in this species. In this study, we examined the antibody response of captive striped skunks (Mephitis mephitis) to ONRAB(®) and tested the protection afforded by the vaccine against rabies virus. Thirty-one skunks were each offered one ONRAB(®) vaccine bait, 25 skunks were administered ONRAB(®) via direct instillation into the oral cavity (DIOC) and ten controls received no vaccine. A blood sample was collected from controls and vaccinates 6 weeks prior to treatment, and then 5 and 7 weeks post-vaccination (PV). A competitive ELISA was used to detect rabies antibody (RAb). Pre-vaccination sera for all skunks, and sera for all controls throughout the serology study, were negative for RAb. Fifty-eight percent (18/31) of skunks in the bait group and 100% (25/25) of skunks that received ONRAB(®) DIOC had detectable RAb by 7 week PV. All 10 controls succumbed to experimental rabies infection. In the group of skunks administered ONRAB(®) DIOC, 100% (23/23) survived challenge 247 days PV. Survival of skunks presented ONRAB(®) baits was 81% (25/31). In the bait group, all 18 skunks that had detectable RAb by 7 week PV survived challenge. Seven additional skunks without detectable RAb prior to week 7 PV also survived. Lack of any remarkable pathology in study animals, together with positive serology and challenge results, supports that ONRAB(®) is a safe and effective oral rabies vaccine for use in skunks.

Oral vaccination and protection of red foxes (Vulpes vulpes) against rabies using ONRAB, an adenovirus-rabies recombinant vaccine.

Twenty-seven red foxes (Vulpes vulpes) were each offered a bait containing ONRAB, a recombinant oral rabies vaccine that uses a human adenovirus vector to express the immunogenic rabies virus glycoprotein; 10 controls received no vaccine baits. Serum samples collected from all foxes before treatment, and each week post-treatment for 16 weeks, were tested for the presence of rabies virus neutralizing antibody (RVNA). In the bait group, a fox was considered a responder to vaccination if serum samples from 3 or more consecutive weeks had RVNA ≥0.5 IU/ml. Using this criterion, 79% of adult foxes (11/14) and 46% of juveniles (6/13) responded to vaccination with ONRAB. Serum RVNA of adults first tested positive (≥0.5 IU/ml) between weeks 1 and 3, about 4 weeks earlier than in juveniles. Adults also responded with higher levels of RVNA and these levels were maintained longer. Serum samples from juveniles tested positive for 1-4 consecutive weeks; in adults the range was 2-15 weeks, with almost half of adults maintaining titres above 0.5 IU/ml for 9 or more consecutive weeks. Based on the kinetics of the antibody response to ONRAB, the best time to sample sera of wild adult foxes for evidence of vaccination is 7-11 weeks following bait distribution. Thirty-four foxes (25 ONRAB, 9 controls) were challenged with vulpine street virus 547 days post-vaccination. All controls developed rabies whereas eight of 13 adult vaccinates (62%) and four of 12 juvenile vaccinates (33%) survived. All foxes classed as non-responders to vaccination developed rabies. Of foxes considered responders to vaccination, 80% of adults (8/10) and 67% of juveniles (4/6) survived challenge. The duration of immunity conferred to foxes would appear adequate for bi-annual and annual bait distribution schedules as vaccinates were challenged 1.5 years post-vaccination.

An assessment of ONRAB oral rabies vaccine persistence in free-ranging mammal populations in Ontario, Canada.

ONRAB is a rabies glycoprotein recombinant human adenovirus type 5 oral vaccine developed for application in baits to control rabies in wildlife populations. Prior to widespread use of ONRAB, both the safety and effectiveness of this vaccine required investigation. While previous research has focused on field performance and the persistence and pathogenicity of ONRAB in captive animals, we sought to examine persistence and shedding of ONRAB in populations of free-ranging target and non-target mammals. We collected oral and rectal swab samples from 84 red foxes, 169 striped skunks, and 116 raccoons during 2007 and 2008 in areas where ONRAB vaccine baits were distributed. We also analyzed 930 tissue samples, 135 oral swab and 138 rectal swab samples from 155 non-target small mammals from 10 species captured during 2008 at sites treated with high densities of ONRAB vaccine baits. Samples were screened for the presence and quantity of ONRAB DNA using quantitative real-time PCR. None of the samples that we analyzed from target and non-target species contained quantities of ONRAB greater than 10(3)EU/mL of ONRAB DNA which is a limit that has previously been applied to assess viral shedding. This study builds on similar research and suggests that replication of ONRAB in animals is short-lived and the likelihood of horizontal transmission to other organisms is low.

Immune response and protection in raccoons (Procyon lotor) following consumption of baits containing ONRAB®, a human adenovirus rabies glycoprotein recombinant vaccine.

We investigated the immune response and protection conferred in raccoons (Procyon lotor) following consumption of ONRAB(®) oral rabies vaccine baits. Forty-two wild-caught, captive raccoons were each offered an ONRAB vaccine bait; 21 controls received no vaccine baits. Blood samples collected from all raccoons before treatment, and each week posttreatment for 16 wk, were assessed for the presence of rabies virus antibody. In the bait group, an individual was considered to have responded to vaccination if serum samples from three or more consecutive weeks were antibody-positive. Using this criterion, 77% (20/26) of raccoons that consumed ONRAB baits with no observed vaccine spillage (full dose) demonstrated a humoral immune response. In the group that received a partial dose (0.05-0.90 mL vaccine recovered), 50% (8/16) of raccoons responded to vaccination. Regardless of the vaccine dose received, among the 28 raccoons that responded to vaccination 18 had antibody initially detectable at week 2 and 22 remained antibody-positive for at least 10 consecutive weeks. Kinetics of the humoral immune response suggest that the best time to conduct postbaiting surveillance for evidence of vaccination would be 6-13 wk following bait deployment, with the highest antibody prevalence expected between weeks 8-10. A sub-sample of 29 raccoons (20 ONRAB, 9 controls) was challenged with raccoon rabies virus variant 350 days posttreatment. Eight of nine controls (89%) developed rabies whereas 15/20 vaccinates (75%) survived. Survival following rabies challenge was significantly higher in raccoons presented ONRAB vaccine baits.

High-density baiting with ONRAB® rabies vaccine baits to control Arctic-variant rabies in striped skunks in Ontario, Canada.

The Arctic variant of rabies virus has been maintained in striped skunks in small foci in southwestern Ontario, Canada, despite the control of the disease in red foxes. To control the disease in skunks, high-density baiting with ONRAB(®) oral rabies vaccine baits was conducted by air and by hand distribution of baits in the vicinity of skunk cases. During 2009, antibody prevalences in skunks were higher in areas baited at a density of 300 baits/km(2) and flight-line spacing of 0.25 km than at 0.5-km spacing. Once an area containing Arctic-variant cases was treated with high densities of ONRAB baits, the disease did not reoccur in skunks in those areas. During 2009, only eight skunks were diagnosed with the Arctic variant of rabies virus in Ontario.

Immunogenicity and efficacy of two rabies vaccines in wild-caught, captive raccoons.

The immunogenicity and efficacy of two rabies vaccines in wild-caught, captive raccoons (Procyon lotor) were investigated. Raccoons were fed Ontario Slim (OS) baits containing a recombinant vaccinia virus-rabies glycoprotein (VRG) oral rabies vaccine, or they were given an intramuscular (IM) injection of IMRAB(®) 3 rabies vaccine. Blood samples collected before treatment and from weeks 1 to 16 posttreatment were assessed for the presence of rabies virus antibody (RVA). There were significantly more positive responders in the group that received an IM injection of IMRAB 3 (18/27) than in the group that consumed VRG in OS baits (VRG-OS; 4/ 26). There were no significant associations among age, sex, and seroconversion. Of those animals that mounted a humoral immune response to vaccination, RVA was first detected between weeks 1 and 5, with the majority of initial seroconversions detectable at week 2. A subsample of 50 raccoons (19 VRG-OS, 18 IMRAB 3, and 13 controls) from the longitudinal serology study was challenged with live raccoon variant rabies virus 442 days after initial treatment. There were significantly more survivors in the group that received IMRAB 3 (13/18) than in the VRG-OS (5/19) or control (2/13) groups. All 15 raccoons that demonstrated a serologic response survived challenge regardless of treatment. Of the 35 raccoons with no detectable serologic response, 30 (86%) succumbed to rabies virus infection (14/15 VRG-OS, 5/7 IMRAB 3, and 11/13 controls).

Field evaluation of an inactivated vaccine to control raccoon rabies in Ontario, Canada.

Since raccoon rabies first appeared in Ontario in 1999, >90,000 raccoons (Procyon lotor) have received IMRAB3 inactivated rabies vaccine via intramuscular (IM) injection and were released at the point of capture as part of a multiyear rabies control program, trap-vaccinate-release (TVR). Of the 132 confirmed cases infected with raccoon-variant rabies virus in Ontario between 1999 and 2005, two were from that vaccinated group, as indicated by the presence of identifying ear tags. During ongoing rabies control programs in 2003, sera were collected from 172 wild raccoons that had received IMRAB3 and tested for rabies-virus antibodies. Raccoons had one of three histories: 1) vaccinated in the current year only (to examine the response to primary vaccination), 2) vaccinated in the previous year only (to determine the duration of the primary antibody response), and 3) vaccinated in the previous year and current year (to examine antibody response to booster vaccination). Seroconversion in primary vaccinates could be detected as early as 1 wk postvaccination when sera were measured with the use of a competitive enzyme-linked immunosorbent assay (C-ELISA) with a cutoff value established to correspond to a neutralizing titer of 0.5 IU/ml. During weeks three and four postvaccination, 94% of sampled raccoons had detectable antibodies to rabies virus and 31% were still antibody positive the following year. Differences in the kinetics of the immune response were found in raccoons sampled from the two different TVR areas of the province. A strong anamnestic response was detected after booster vaccinations. IMRAB3 by IM injection was found to be an efficacious vaccine for rabies control in raccoons.

Aerial distribution of ONRAB baits as a tactic to control rabies in raccoons and striped skunks in Ontario, Canada.

During August 2006 and 2007, baits containing oral rabies vaccine, live adenovirus vector, known as ONRAB , were aerially distributed in SW Ontario, Canada. Bait acceptance during 2006 was 62 and 74% in raccoons (Procyon lotor) in areas baited at 150 baits/km(2) and 75 and 77% in plots baited at 300 baits/km(2). During 2007, bait acceptance for raccoons ranged between 59% and 80%, and 83% and 87%, in areas baited at 75 and 400 baits/km(2), respectively. Bait acceptance by skunks varied among plots (5-24%). Rabies virus-specific seroconversion during 2006 averaged 66 and 81% in raccoons in areas baited at 150 and 300 baits/km(2), respectively. During 2007, seroconversion by raccoons was 76 and 84% in areas baited at 75 and 400 baits/km(2), respectively. Seroconversion by skunks varied among plots (17-51%). Vaccine efficacy, as judged by the percentage of animals that consumed a bait and seroconverted, averaged 79 and 87% during 2006 for raccoons in areas baited at 150 and 300 baits/km(2), respectively, and 81 and 90% in areas baited during 2007 at 75 and 400 baits/km(2), respectively. Because tetracycline marking was poor in skunks, an estimate of vaccine efficacy was not possible. Aerial distribution of ONRAB vaccine baits seems to be a feasible tactic for controlling rabies in skunks and raccoons.

Prevalence of tetracycline and rabies virus antibody in raccoons, skunks, and foxes following aerial distribution of V-RG baits to control raccoon rabies in Ontario, Canada.

More than 3.6 million baits containing a recombinant vaccinia virus-rabies glycoprotein (V-RG) oral rabies vaccine were aerially or hand-distributed during 1999-2006 in an approximate 4,000-9,000 km(2) area of eastern Ontario, Canada, as part of a multitactic approach to control the raccoon variant of rabies. The efficacy of the program was assessed through the collection and testing of > 6,900 animals for bait acceptance and rabies virus-specific antibodies. Raccoon acceptance of rabies vaccine baits was significantly greater (71-83% ) in areas baited at a density of 150 baits/km(2) compared to areas baited at 75 baits/km(2) (26-58% ), and more raccoons consumed vaccine baits in areas baited with a flight line spacing of 0.75 km (45.3% [321/708]) than with a spacing of 1.5 km (33.8% [108/320]). In addition, greater numbers of raccoons consumed vaccine baits during a drop in September (52.7% [213/404]) as opposed to a June bait drop (34.6% [216/624]). Seropositivity rates for raccoons ranged between 7% and 28% in areas baited at 75/km(2) and 10% to 27% in areas baited at 150/km(2) with statistical differences varying among years and treatments. The last case of raccoon-variant rabies reported in Ontario was in September 2005. The control of raccoon rabies in Ontario has resulted in an estimated $6M to $10 M Cdn annual savings in rabies-associated costs.

Characterization of a functional relationship between hepatocyte growth factor and mouse bone marrow-derived mast cells.

During the early stage (at 4 weeks) of interleukin-3 (IL-3)-induced development, mouse bone marrow-derived mast cells (BMMC) express alpha 4, alpha 5 and alpha 6 integrins, whereas with further maturation beyond 10 weeks, only alpha 5 integrin remains stably expressed. Hepatocyte growth factor (HGF) modulates the growth and movement of diverse cell types upon binding to its receptor, encoded by the proto-oncogene c-met. We report here the expression of c-met by BMMC throughout the course of their development. In addition, HGF stimulated migration of early week-4 BMMC, but not of the later stage week-10 BMMC, on fibronectin and laminin substrates. The developmental stage-dependent effect of HGF on BMMC was due to specific stimulation of the migratory function of alpha 4 and alpha 6, but not alpha 5 integrins. In addition, HGF had no effect on BMMC growth, either alone or in combination with IL-3. While HGF is stimulatory of the migratory function of BMMC, our results show that BMMC in turn can modulate HGF function. Thus, upon activation via the IgE receptors, BMMC released proteases that abolished HGF activities. Analyses of the degradation products by two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot using antisera prepared against recombinant HGF and the kringle 3 domain of HGF revealed specific degradation of HGF alpha but not beta/beta' subunits. Therefore, our results suggest that: 1) the motogenic effect of HGF on BMMC varies according to the stage of their development, 2) HGF stimulation of BMMC migration is due to selective activation of alpha 4 and alpha 6, but not alpha 5 integrin function, and 3) there exists a two-way relationship between BMMC and HGF such that HGF stimulates the beta 1 integrin-mediated migratory function of BMMC, which can, in turn, modulate HGF function by release of serine proteases.

Differential utilization of VLA-4 (alpha 4 beta 1) and -5 (alpha 5 beta 1) integrins during the development of mouse bone marrow-derived mast cells.

Cytokines have been shown to have major roles in the development of mast cells from bone marrow progenitors. Immature mast cells derived from bone marrow thus leave the blood system to complete their course of maturation within tissues. However, it is now clear that VLA (beta 1) integrins with function in mediating cell-cell and cell-extracellular matrix protein interactions have effects on the growth and differentiation of diverse cell types. At present, the involvement of VLA integrins during mast cell development is still unclear. In this study, we report the preparation of a new monoclonal antibody (mAb) against mouse VLA-5 (alpha 5 beta 1) integrin. Together with mAb R1-2, we characterized the expression of VLA-4 (alpha 4 beta 1) and VLA-5 integrins, the two major fibronectin receptors, on two long-term cultured mast cell lines, CFTL-15 and MC/9. CFTL-15 cells were found to express both VLA-4 and -5 integrins whereas MC/9 cells expressed only VLA-5 but not VLA-4. We speculated that VLA integrin expression may be related to mast cell development. Thus bone marrow-derived mast cells (BMMC) were characterized after varying periods of development induced by IL-3. During the first 3 weeks the expression of VLA-4 and VLA-5 increased progressively and both were involved in mediating adhesion of BMMC to fibronectin. At time periods of greater than 3 weeks, the expression of VLA-4 declined gradually to little, if any, by week 13. In comparison, VLA-5 remained stably expressed and functioned as the major receptor for fibronectin. Results from this study therefore suggest that BMMC differentially utilize VLA-4 and VLA-5 integrins during IL-3-induced development. Differential expression of VLA integrins may have effects on the recirculation properties, tissue distribution and eventual maturation of progenitors to fully matured mast cells.

Integrin VLA-6 (alpha 6 beta 1) mediates adhesion of mouse bone marrow-derived mast cells to laminin.

The development of mast cells from bone marrow precursors and their function as the mucosal- or connective-tissue-type mast cell are critically dependent on microenvironmental factors. Extracellular matrix proteins, such as collagen, fibronectin, and laminin, may represent insoluble components of the microenvironment. Recent studies have described multiple isoforms of laminin isolated from different tissues. In the present study, adhesion of mouse bone marrow-derived mast cells (BMMC) and long-term mast cell lines to Engelbreth-Holm-Swarm (EHS) tumor laminin, rat laminin, human merosin, and human placental laminin was compared. The greatest level of adhesion was found with human laminin as the substrate. By use of a newly prepared mouse VLA-alpha 6 integrin-specific mAb (MA6) together with the previously described mAb GoH3, VLA-6 (alpha 6 beta 1) integrin was found to be expressed and utilized by BMMC and long-term mast cell lines. VLA-6 has been described as a major laminin receptor with roles in diverse cell functions including cell growth and differentiation. BMMC have been shown to express a 32/67-kDa laminin receptor. Therefore, in addition to the 32/67-kDa laminin receptor described in early studies, BMMC also express VLA-6 integrin, which may have roles in the regulation of their development.