Establishment of a model of Mycoplasma hyopneumoniae infection using Bama miniature pigs

Development and Characterization of a Primary Ciliated Porcine Airway Model for the Evaluation of In Vitro Mucociliary Clearance and Mucosal Drug Delivery

Background/Objectives: In vitro models play a crucial role in preclinical respiratory research, enabling the testing and screening of mucosal formulations, dosage forms, and inhaled drugs. Mucociliary clearance (MCC) is an essential defense mechanism in mucosal drug delivery but is often impaired in respiratory diseases. Despite its importance, standardized in vitro MCC assays are rarely reported. Furthermore, many published methods primarily measure cilia beat frequency (CBF), which requires high-speed cameras that are not accessible to all laboratories. Therefore, this study aimed to develop a physiologically relevant, differentiated in vitro model of the respiratory epithelium that incorporates both beating cilia and functional MCC. We chose porcine airway mucosa as an alternative to human tissue due to ethical considerations and limited availability. The established model is designed to provide a reproducible and accessible method for a broad range of research laboratories. Methods: The previously published tracheal mucosal primary cell (TMPC DS) model, derived from porcine tissue, lacked the presence of beating cilia, which are crucial for effective MCC analysis. For accurate MCC assessment, beating cilia are essential as they play a key role in mucus clearance. To address this limitation, the here-described ciliated tracheal mucosal primary cell (cTMPC) model was developed. cTMPCs were isolated from porcine tissue and cultured under air-liquid interface (ALI) conditions for 21 days to promote differentiation. This model was evaluated for cell morphology, tight junction formation, ciliated and mucus-producing cells, barrier function, gene expression, and tracer/IgG transport. MCC and the model's suitability for standardized MCC assays were assessed using an inverted microscope. In contrast to the TMPC DS model, which lacked beating cilia and thus could not support MCC analysis, the cTMPC model allows for comprehensive MCC studies. Results: The developed differentiated in vitro model demonstrated key structural and functional features of the respiratory epithelium, including well-differentiated cell morphology, tight junction integrity, ciliated and mucus-producing cells, and effective barrier function. Functional MCC was observed, confirming the model's potential for standardized clearance assays. Conclusions: This differentiated in vitro model closely replicates the structural and functional characteristics of in vivo airways. It provides a valuable platform for studying mucociliary clearance, toxicology, drug uptake, and evaluating mucosal formulations and dosage forms in respiratory research.

Structure and function relationships of mucociliary clearance in human and rat airways

Mucociliary clearance is a vital defense mechanism of the human airways, protecting against harmful particles and infections. When this process fails, it contributes to respiratory diseases like chronic obstructive pulmonary disease (COPD) and asthma. While advances in single-cell transcriptomics have revealed the complexity of airway composition, much of what we know about how airway structure impacts clearance relies on animal studies. This limits our ability to create accurate human-based models of airway diseases. Here we show that the airways in female rats and in humans exhibit species-specific differences in the distribution of ciliated and secretory cells as well as in ciliary beat, resulting in significantly higher clearance effectiveness in humans. We further reveal that standard lab-grown cultures exhibit lower clearance effectiveness compared to human airways, and we identify the underlying structural differences. By combining diverse experiments and physics-based modeling, we establish universal benchmarks to assess human airway function, interpret preclinical models, and better understand disease-specific impairments in mucociliary clearance.

Structure and Function Relationships of Mucociliary Clearance in Human and Rat Airways

Mucociliary clearance is a vital defense mechanism of the human airways, protecting against harmful particles and infections. When this process fails, it contributes to respiratory diseases like chronic obstructive pulmonary disease (COPD) and asthma. While advances in single-cell transcriptomics have revealed the complexity of airway composition, much of what we know about how airway structure impacts clearance relies on animal studies. This limits our ability to create accurate human-based models of airway diseases. Here we show that the airways in female rats and in humans exhibit species-specific differences in the distribution of ciliated and secretory cells as well as in ciliary beat, resulting in significantly higher clearance effectiveness in humans. We further reveal that standard lab-grown cultures exhibit lower clearance effectiveness compared to human airways, and we identify the underlying structural differences. By combining diverse experiments and physics-based modeling, we establish universal benchmarks to assess human airway function, interpret preclinical models, and better understand disease-specific impairments in mucociliary clearance.

[Veterinary care for minipigs - a challenge for small animal practice]

Miniature pet pigs, called Minipigs, were originally bred for experimental purposes. Since the 1990s, they have been kept as pets in private households. They are kept indoor, in stables with runs and outdoors. Mistakes in feeding and insufficient knowledge of pet owners about their animals lead to husbandry-related diseases. Veterinary practices for small animals are often visited in the case of disease or necessary care measures. In this review, the topics of breeding lines, husbandry, feeding, legal principles, clinical examination, the most important diseases and their treatment are presented.

Characterization of a primary cellular airway model for inhalative drug delivery in comparison with the established permanent cell lines CaLu3 and RPMI 2650

Purpose

For optimization of respiratory drug delivery, the selection of suitable in vitro cell models plays an important role in predicting the efficacy and safety of (bio)pharmaceutics and pharmaceutical formulations. Therefore, an in-depth comparison of different primary and permanent in vitro cellular airway models was performed with a focus on selecting a suitable model for inhalative antibodies.

Methods

Primary cells isolated from the porcine trachea were compared with the established human cell lines CaLu3 and RPMI 2650. The in vitro models were characterized for different epithelial markers by real-time quantitative polymerase chain reaction, which provides insight into the cellular composition of each model. For a few selected markers, the results from RT-qPCR were confirmed via immunofluorescence. Barrier integrity was assessed by transepithelial electrical resistance measurements and FITC-dextran permeability.

Results

Primary cell models retain key features of the respiratory epithelium, e.g., the formation of a tight epithelial barrier, mucin production, and the presence of club/basal cells. Furthermore, the expression of Fc receptors in the primary cell models closely resembles that in respiratory mucosal tissue, an essential parameter to consider when developing therapeutic antibodies for inhalation.

Conclusion

The study underlines the importance of selecting wisely appropriate in vitro models. Despite the greater effort and variability in cultivating primary airway cells, they are far superior to permanent cells and a suitable model for drug development.

Supplementary Information

The online version contains supplementary material available at 10.1007/s44164-024-00079-y.

STRUCTURE-FUNCTION RELATIONSHIPS OF MUCOCILIARY CLEARANCE IN HUMAN AIRWAYS

Our study focuses on the intricate connection between tissue-level organization and ciliated organ function in humans, particularly in understanding the morphological organization of airways and their role in mucociliary clearance. Mucociliary clearance is a key mechanical defense mechanism of human airways, and clearance failure is associated with many respiratory diseases, including chronic obstructive pulmonary disease (COPD) and asthma. While single-cell transcriptomics have unveiled the cellular complexity of the human airway epithelium, our understanding of the mechanics that link epithelial structure to clearance function mainly stem from animal models. This reliance on animal data limits crucial insights into human airway barrier function and hampers the human-relevant in vitro modeling of airway diseases. This study, for the first time, maps the distribution of ciliated and secretory cell types along the airway tree in both rats and humans, noting species-specific differences in ciliary function and elucidates structural parameters of airway epithelia that predict clearance function in both native and in vitro tissues alike. By uncovering how tissue organization influences ciliary function, we can better understand disruptions in mucociliary clearance, which could have implications for various ciliated organs beyond the airways.

A porcine circovirus type 2d-based virus-like particle vaccine induces humoral and cellular immune responses and effectively protects pigs against PCV2d challenge

The pathogenic porcine circovirus type 2 (PCV2) leads to significant economic losses in pig production. PCV2d is currently the dominant genotype causing porcine circovirus-associated disease (PCVAD) worldwide. Therefore, development of a recombinant PCV2d-based vaccine is required to elicit complete protection against PCV2d infection. In this study, we generated virus-like particles of PCV2d-based capsid protein (Bac-2dCP) using a baculovirus expression system and evaluated its protective efficacy against PCV2d infection in specific pathogen-free (SPF) pigs. Three-week-old SPF miniature pigs were intramuscularly immunized with purified Bac-2dCP and intranasally challenged with PCV2d at 4 weeks post-vaccination. The Bac-2dCP group showed significantly higher IgG levels and neutralizing antibodies against PCV2b and PCV2d genotypes, as well as increased interferon-γ levels, and increased body weight and average daily weight gain compared with positive (challenged) and negative (unchallenged) controls. In particular, the Bac-2dCP group showed almost complete absence of PCV2d DNA in serum, nasal, and rectal swabs and in lung, lymph node, and kidney tissue samples. However, the positive control group exhibited low levels of neutralizing antibody, and high levels of PCV2 DNA in serum, swab, and tissue samples, resulting in PCV2-associated pathological lesions. The results of this study demonstrated that a recombinant Bac-2dCP vaccine conferred complete protection against a PCV2d challenge in SPF miniature pigs.

Pathological Evaluation of Porcine Circovirus 2d (PCV2d) Strain and Comparative Evaluation of PCV2d and PCV2b Inactivated Vaccines against PCV2d Infection in a Specific Pathogen-Free (SPF) Yucatan Miniature Pig Model

Porcine circovirus type 2 (PCV2) is an economically important swine pathogen that causes porcine circovirus-associated diseases (PCVADs). The objective of this study was to evaluate the use of specific pathogen-free Yucatan miniature pigs (YMPs) as an experimental model for PCV2d challenge and vaccine assessment because PCV2-negative pigs are extremely rare in conventional swine herds in Korea. In the first experiment, every three pigs were subjected to PCV2d field isolate or mock challenge. During three weeks of experiments, the PCV2d infection group exhibited clinical outcomes of PCVAD with high viral loads, lymphoid depletion, and detection of PCV2d antigens in lymphoid organs by immunohistochemistry. In the second experiment, three groups of pigs were challenged with PCV2d after immunization for three weeks: a nonvaccinated group (three pigs), a PCV2b-Vac group vaccinated with a commercial PCV2b-based inactivated vaccine SuiShot^® Circo-ONE (five pigs), and a PCV2d-Vac group vaccinated with an experimental PCV2d-based inactivated vaccine (five pigs). During the three weeks of the challenge period, nonvaccinated pigs showed similar clinical outcomes to those observed in the PCV2d infection group from the first experiment. In contrast, both the PCV2b and PCV2d vaccinations produced good levels of protection against PCV2d challenge, as evidenced by reduced viral loads, improved growth performance, high virus-neutralizing antibody titers, and less development of PCV2-associated pathological lesions. Taken together, these data suggest that YMPs could be an alternative model for PCV2 challenge experiments, and these animals displayed typical clinical and pathological features and characteristics of protective immunity induced by the vaccines that were consistent with those resulting from PCV2 infections in conventional pigs.