The neonatal Fc receptor (FcRn) is a key determinant of IgG homeostasis. It binds to the Fc domain of IgG in a strictly pH-dependent manner and protects IgG from lysosomal degradation. The impact of FcRn salvage pathway on IgG monoclonal antibody (mAb) pharmacokinetics (PK) has been well established. In this report, a set of mAbs with wild-type human Fc sequences but different Fab domains were used to examine the potential impact of Fab domain on in vitro FcRn binding and in vivo PK. We were surprised to find that mAbs with the same wild-type human Fc sequences but different Fab domains were shown to bind FcRn with considerable differences in both the binding at acidic pH and the dissociation at neutral pH, suggesting that the Fab domain may also have an impact on FcRn interaction. For these mAbs, no relationship between the FcRn binding affinity at acidic pH and in vivo PK was found. Instead, an apparent correlation between the in vitro FcRn dissociation at neutral pH and the in vivo PK in human FcRn mice, nonhuman primates and humans was observed. Our results suggested that the Fab domain of mAbs can affect their interaction with FcRn and thus their pharmacokinetic properties and that in vitro FcRn binding/dissociation assays can be a useful screening tool for pharmacokinetic assessment of mAbs with wild-type Fc sequences.

https://dmd.aspetjournals.org/content/dmd/early/2011/05/24/dmd.111.039453.full.pdf

Monoclonal Antibodies with Identical Fc Sequences Can Bind to FcRn Differentially with Pharmacokinetic Consequences

Chlamydia (C.) psittaci is an economically relevant pathogen in poultry and pet birds, where it causes psittacosis/ornithosis, and also a human pathogen causing atypical pneumonia after zoonotic transmission. Despite its well-documented prevalence, the agent has received less attention by researchers than other Chlamydia spp. in the last decades. In the present paper, we review recently published data on C. psittaci infection and attempt to single out characteristic features distinguishing it from related chlamydial agents. It is remarkable that C. psittaci is particularly efficient in disseminating in the host organism causing systemic disease, which occasionally can take a fulminant course.

 At the cellular level, the pathogen's broad host cell spectrum (from epithelial cells to macrophages), its rapid entry and fast replication, proficient use of intracellular transport routes to mitochondria and the Golgi apparatus, the pronounced physical association of chlamydial inclusions with energy-providing cell compartments, as well as the subversive regulation of host cell survival during productive and persistent states facilitate the characteristic efficient growth and successful host-to-host spread of C. psittaci.

 At the molecular level, the pathogen was shown to upregulate essential chlamydial genes when facing the host immune response. We hypothesize that this capacity, in concert with expression of specific effectors of the type III secretion system and efficient suppression of selected host defense signals, contributes to successful establishment of the infection in the host.

 Concerning the immunology of host–pathogen interactions, C. psittaci has been shown to distinguish itself by coping more efficiently than other chlamydiae with pro-inflammatory mediators during early host response, which can, to some extent, explain the effective evasion and adaptation strategies of this bacterium.

 We conclude that thorough analysis of the large number of whole-genome sequences already available will be essential to identify genetic markers of the species-specific features and trigger more in-depth studies in cellular and animal models to address such vital topics as treatment and vaccination.

/pdf/chlamydia-psittaci-update-on-an-underestimated-zoonotic-2zpip6mtpy.pdf

Chlamydia psittaci: update on an underestimated zoonotic agent.

Pneumonia is a major cause of disease and death in foals. Rhodococcus equi, a gram-positive facultative intracellular pathogen, is a common cause of pneumonia in foals. This article reviews the clinical manifestations of infection caused by R. equi in foals and summarizes current knowledge regarding mechanisms of virulence of, and immunity to, R. equi. A complementary consensus statement providing recommendations for the diagnosis, treatment, control, and prevention of infections caused by R. equi in foals can be found in the same issue of the Journal.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1939-1676.2011.00804.x

Rhodococcus equi: Clinical Manifestations, Virulence, and Immunity

Rhodococcus equi, a gram-positive facultative intracellular pathogen, is one of the most common causes of pneumonia in foals. Although R. equi can be cultured from the environment of virtually all horse farms, the clinical disease in foals is endemic at some farms, sporadic at others, and unrecognized at many. On farms where the disease is endemic, costs associated with morbidity and mortality attributable to R. equi may be very high. The purpose of this consensus statement is to provide recommendations regarding the diagnosis, treatment, control, and prevention of infections caused by R. equi in foals.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1939-1676.2011.00835.x

Diagnosis, treatment, control, and prevention of infections caused by Rhodococcus equi in foals.

Macrolides are a group of antibiotics that have been widely used in human medical and veterinary practices. Analysis of macrolides and related compounds in food, biological, and environmental matrices continue to be the focus of scientists for the reasons of food safety, pharmacokinetic studies, and environmental concerns. This article presents an overview on the primary biological properties of macrolides and their associated analytical issues, including extraction, liquid chromatography-mass spectrometry (LC-MS), method validation, and measurement uncertainty. The main techniques that have been used to extract macrolides from various matrices are solid-phase extraction and liquid-liquid extraction. Conventional liquid chromatography (LC) with C18 columns plays a dominant role for the determination of macrolides, whereas ultra-performance liquid chromatography (UPLC) along with sub-2 microm particle C18 columns reduces run time and improves sensitivity. Mass spectrometry (MS), serving as a universal detection technique, has replaced ultraviolet (UV), fluorometric, and electrochemical detection for multi-macrolide analysis. The triple-quadrupole (QqQ), quadrupole ion trap (QIT), triple-quadrupole linear ion trap, time-of-flight (TOF), and quadrupole time-of-flight (QqTOF) mass spectrometers are current choices for the determination of macrolides, including quantification, confirmation, identification of their degradation products or metabolites, and structural elucidation. LC or UPLC coupled to a triple-quadrupole mass spectrometer operated in the multiple-reaction monitoring (MRM) mode (LC/MS/MS) is the first choice for quantification. UPLC-TOF or UPLC-QqTOF has been recognized as an emerging technique for accurate mass measurement and unequivocal identification of macrolides and their related compounds.

Analysis of macrolide antibiotics, using liquid chromatography-mass spectrometry, in food, biological and environmental matrices.

Mass antimicrobial treatment of foals with small ultrasonographic pulmonary lesions is common on farms with endemic disease caused by Rhodococcus equi. The objectives of this study were to compare the relative efficacy of three antimicrobial protocols for the treatment of pulmonary abscesses on a farm with endemic infections caused by R. equi and to determine the frequency of spontaneous resolution of subclinical pulmonary lesions. Foals with ultrasonographic evidence of pulmonary abscesses ≥ 1.0 cm in diameter (n=128) were randomly allocated to one of four equal treatment groups. Animals with respiratory distress or severe pulmonary lesions were excluded from the study. Treatment groups consisted of: (1) tulathromycin intramuscularly; (2) azithromycin monotherapy orally; (3) azithromycin in combination with rifampin orally; and (4) glucose orally as a placebo. Physical examination, thoracic ultrasonography and white blood cell (WBC) counts were performed weekly by individuals unaware of treatment group assignment. Foals that worsened were removed from the study and treated with azithromycin and rifampin. Overall, 14/32 (43.8%) foals in the placebo group recovered without the need for therapy. The proportion of foals that responded to the initial therapy, the duration of therapy, the kinetics of ultrasonographic lesion resolution, the proportion of foals that had to be removed from the study and the number of days to removal from the study did not differ significantly between treatment groups. The study showed that many foals with pulmonary abscesses recover without antimicrobial therapy. Moreover, treatment of sub-clinically affected foals with antimicrobial agents did not significantly hasten recovery.

Failure of antimicrobial therapy to accelerate spontaneous healing of subclinical pulmonary abscesses on a farm with endemic infections caused by Rhodococcus equi.

The delivery of clarithromycin (CRL) to its site of action in bronchial/alveolar epithelial cells (EC), bronchial epithelial lining fluid (ELF), and bronchoalveolar lavage cells (BALC) may be influenced by CYP3A4 and the drug transporters, ATP-binding cassette (ABC) B1 and ABCC2 and organic anion-transporting polypeptides (OATPs), which can be modulated and/or up-regulated via the nuclear pregnane X receptor (PXR) by rifampicin (RIF). Therefore, we evaluated the disposition and pulmonary distribution of CLR (7.5 mg/kg b.i.d., 21 days) and expression of ABCB1, ABCC2, OATP1A2, and OATP2B1 in EC and BALC before and after comedication of RIF (10 mg/kg b.i.d., 11 days) in nine healthy foals (41–61 days, 115–159 kg) in which the genetic homology of drug transporters is close to that of their human analogs. After RIF comedication, relative bioavailability of CLR decreased by more than 90%. Concentrations in plasma (29.8 ± 26.3 versus 462 ± 368 ng/ml), ELF (0.69 ± 0.66 versus 9.49 ± 6.12 μg/ml), and BALC (10.2 ± 10.2 μg/ml 264 ± 375 μg/ml; all P < 0.05) were lowered drastically, whereas levels of the metabolite 14-hydroxyclarithromycin were not elevated despite higher 4β-hydroxycholesterol/cholesterol plasma concentration ratio, a surrogate for CYP3A4 induction. In the presence of CLR, ABCC2 and PXR mRNA contents were significantly and coordinately ( r 2 = 0.664, P < 0.001) reduced in BALC after RIF. In EC, mRNA expression of OATP1A2 increased but that of OATP2B1 decreased (both P < 0.05). RIF interrupts oral absorption and decreases CRL plasma levels below the minimal inhibitory concentration for eradication of Rhodococcus equi . Evidence that RIF influences the cellular uptake of CLR in bronchial cells and the PXR expression in BALC in the presence of high CLR concentrations exists.

https://dmd.aspetjournals.org/content/dmd/early/2011/06/20/dmd.111.039206.full.pdf

Oral Absorption of Clarithromycin Is Nearly Abolished by Chronic Comedication of Rifampicin in Foals

Tulathromycin is a new injectable macrolide antibiotic used for the treatment of pulmonary diseases of swine and cattle. In this study, 37 foals with sonographic evidence of lung abscesses were treated with tulathromycin (2.5mg/kg intramuscularly [IM] once weekly, group 1) and 33 foals (group 2) with a combination of azithromycin (10mg/kg per os [PO] once daily for the first seven days of therapy, thereafter every other day) and rifampin (10mg/kg PO twice daily). The bacterial aetiological agent was not determined. The foals were only mildly sick and the median number of pulmonary abscesses was 1.4 (group 1) and 1.6 (group 2). Thirty foals in each group were treated without modifying therapy protocols until all clinical signs of disease had subsided. Tulathromycin was administered for a mean of 53 days, and azithromycin/rifampin for 42 days. The following side effects were associated with tulathromycin (279 IM injections): self-limiting diarrhoea in 11 foals; elevated temperature in six foals, and swellings at the injection site in 12 foals. This study provides some evidence that tulathromycin is well tolerated and appears promising for the treatment of pulmonary abscesses in foals.

Evaluation of tulathromycin in the treatment of pulmonary abscesses in foals.

Quantitative determination of the macrolide antibiotic tulathromycin in plasma and broncho-alveolar cells of foals using tandem mass spectrometry

The prophylactic application of azithromycin to prevent pulmonary abscesses in foals was evaluated on a stud with endemic Rhodococcus equi pneumonia Forty-five foals served as untreated controls in two groups Twenty-five foals were given azithromycin (10 mg/kg) orally once daily for 4 weeks The foals were examined once a week from birth to the age of 5 months If clinical signs or leucocytosis were noted and pulmonary sonographic findings (diameter >10 mm) were observed, the diagnosis of abscessing pneumonia was made The prevalence of pulmonary abscesses was similar in the control groups (31/45 foals), and in the azithromycin group (15/25 foals), but the foals in the azithromycin group were affected significantly later (median: day 83, range 67–123 days) (control groups: day 54, range 52–82; and 46, range 28–86 days) It was concluded that the application of azithromycin for 28 days post-natally does not reduce the prevalence of pulmonary abscesses in foals on a stud with endemic pneumonia

Monica Venner

Papers

Failure of antimicrobial therapy to accelerate spontaneous healing of subclinical pulmonary abscesses on a farm with endemic infections caused by Rhodococcus equi.

Oral Absorption of Clarithromycin Is Nearly Abolished by Chronic Comedication of Rifampicin in Foals

Evaluation of tulathromycin in the treatment of pulmonary abscesses in foals.

Quantitative determination of the macrolide antibiotic tulathromycin in plasma and broncho-alveolar cells of foals using tandem mass spectrometry

Efficacy of azithromycin in preventing pulmonary abscesses in foals.