An asymptotic description of a basic FcRn-regulated clearance mechanism and its implications for PBPK modelling of large antibodies.

A basic FcRn-regulated clearance mechanism is investigated using the method of matched asymptotic expansions. The broader aim of the work is to obtain further insight on the mechanism, thereby providing theoretical support for future pharmacologically-based pharmacokinetic modelling efforts. The corresponding governing equations are first non-dimensionalised and the order of magnitudes of the model parameters are assessed based on their values reported in the literature. Under the assumption of high FcRn-binding affinity, analytical approximations are derived that are valid over the characteristic phases of the problem. Additionally, relatively simple equations relating clearance and AUC to physiological model parameters are derived, which are valid over the longest characteristic time scale of the problem. For lower to moderate doses clearance is effectively linear, whereas for higher doses it is nonlinear. It is shown that for all doses sufficiently high the leading-order approximation for the IgG concentration in plasma, over the longest characteristic time scale, is independent of the initial dose. This is because IgG that is in 'excess' of FcRn is eliminated over a time scale much shorter than that of the terminal phase. In conclusion, analytical approximations of the basic FcRn mechanism have been derived using matched asymptotic expansions, leading to a simple equation relating clearance to FcRn binding affinity, the ratio of degradation and FcRn concentration, and the volumes of the system.

Hygiene assessments of school kitchens based on the microbiological status of served food.

BACKGROUND: According to European trends, more children eat at school canteens than ever before, therefore food safety and quality have become increasingly significant in recent years. Nevertheless, there are large differences in food safety levels in different school canteens. We hypothesize that the microbial status of the served meal represents on the general hygiene of the kitchen. Our research examines whether mesophilic aerobic bacteria measured in served food are connected with the level of hygiene in the catering unit, and whether this indicator can be used as a criterion for assessing school kitchens. METHODS: Meal samples were collected from six school kitchens, and mesophilic aerobic bacterial count was measured. Samples were collected on five different days, so each kitchen was monitored five times. Two meals per visit were collected: a soup and a main course. RESULTS: Out of the 60 samples, 26 were good (CFU/g < 103), 24 were acceptable (CFU/g: 103–105), and in 10 samples, the microbial count was found to be above the limit (CFU/g > 105). Statistical calculations revealed that microbial contamination of served meals was influenced neither by the supplier nor by the type of meal (soup or main course). However, the level of hygiene in the serving kitchen significantly affects the microbial status of meals. CONCLUSIONS: Based on the results, a qualification system can be developed using the mesophilic aerobic bacterial count measurable in the served meal to assess hygiene. By regular determination of mesophilic aerobic bacterial count and the presence of Enterobacteriaceae, the food safety of a catering unit can be quantitatively evaluated.

Dynamics of 125I-labelled horse serum albumin presentation in vivo in guinea pigs.

Low antibody production in guinea-pig sera was determined by passive hemagglutination after 125I-labelled horse serum albumin (HoSA) injection. The appearance of radiolabelled HoSA on T cells, B cells and monocytes/macrophages (Mo) of guinea pigs was detected and followed as a function of time. The radioactivity peaks appeared first on B cells and Mo, later on the T cells. The circulating T lymphocytes contained labelled antigen 7 days after the injection while T and B lymphocytes in the spleen preserved their radioactivity 15 and 20 days later. Helper, suppressor and effector T cells were able to fix 125I-HoSA, this was shown by autoradiography using monoclonal antibodies 4 days following the antigen injection.

Antigen-specific lymphocyte clone elimination and reappearance in guinea pigs using 125I-labelled horse serum albumin.

T cells in the blood and spleen of guinea pigs fixed significantly higher quantities of radiolabelled antigen on day 4 following injection than did B cells or macrophages. Fixed radioactivity produced continuous radiation damage on the cells involved and the antigen-specific lymphocyte clone disappeared. This was shown by the absence of antibody production in the sera determined by passive haemagglutination. The reappearance of the specific lymphocyte clone required more than 20 days.

Inhibition of anaphylaxis by inactivated lymphocyte clone with radiolabelled antigen.

125I-labelled ovalbumin (OVA) antigen did not sensitize guinea-pigs and anaphylaxis did not develop after native OVA challenge. The radiolabelled antigen was fixed by lymphocytes with highly specific receptors for 125I-OVA and this condition produced a continuous radiation damage leading to inactivation of the cells. As the proliferative response of lymphocytes did not occur, no antibody production was detected. This was demonstrated by passive haemagglutination techniques. However, the immune response to a simultaneously given non-radioactive antigen remained intact. It is supposed that radiation damage depended on specific activity of antigen destroying the antigen-specific lymphocyte clone selectively. The mechanism and the practical importance of the in vivo 'antigen suicide' is discussed.

Functional heterogeneity of macrophages.

The antibody-binding activities of rabbit peritoneal macrophages separated on discontinuous gradients of Ficoll were investigated. The antibody was rabbit anti-ovalbumin IgG labelled with 125I. Of the five fractions obtained, one macrophage fraction was found to bind substantially more antibody than the others. These macrophages possessed more Fc receptor sites than the others and the number of Fc receptors (n) and the association constant (K) of these cells was calculated. By electron microscopy, the phagocytic activity of the subpopulation with most Fc receptors was less than that of the others.

Detection of thymosin 5 in calf and mouse thymus and in nude mouse dysgenetic thymus.

Thymosin 5 was traced in calf and mouse thymuses by fluorochrome-labelled rabbit anti-calf thymosin. The presence of thymosin 5 or its individual components was found 1. in groups of cortical epithelial cells in calf thymuses and in single cortical epithelial cells in mouse thymuses. 2. In some marginal (blastema) cells of the thymus cortex of calves and 14-day-old mice. 3. In perivascular epithelial cells of the calf thymus. 4. In occasional medullary epithelial cells of the calf and mouse thymus. In all cases there was a marked alternation of entirely negative and positive cell-containing thymic lobuli. In 4 of 13 cases comparatively strong positivity was found in tightyly arranged epithelial cells in an individual acinus in the dysgenetic thymus of nude mice, the positive cases being concentrated among the youngest mice studied.

Effects of disodium chromoglycate on systemic anaphylaxis in guinea pigs, rats and mice.

Disodium chromoglycate (DSCG) exerted a protective action in passively-sensitized guinea pigs undergoing anaphylaxis but no such effect was found in actively-sensitized animals. The degree of protection depended on the route and the time of administration. DSCG also protected actively-sensitized rats undergoing anaplylaxis but no effect was found in mice.

The effect of continuous human lymphokine treatment on skin graft rejection in mice.

Continuous intraperitoneal treatment with human lymphokines produced by Con-A stimulated peripheral human lymphocytes caused the acceleration of skin graft rejection in mice.

Platelet activating factor, the trigger of haemostatic alterations in rat anaphylaxis.

Platelet-activating factor (PAF) generated by an IgE-mediated reaction in the peritoneal cabity of rats was partially purified by adsorption to diatomaceous earth. It aggregated rat platelets and, as a consequence, activated Hageman factor in in vitro, as well as in vivo, conditions. The haemostatic alterations induced by PAF showed similarity to those observed in the early phase of rat anaphylaxis.

Platelets in rat anaphylaxis.

The number of circulating platelets dropped abruptly in the early phase of severe anaphylactic shock (AS) of the rat and could be inhibited by Persantin but not by heparin pretreatment. The results strongly suggest that an aggregating agent, perhaps "platelet aggregating factor", formed or released during anaphylaxis is responsible for the decrease of platelet number. The organ distribution of 51Cr labelled platelets showed that in AS the aggregated platelets were removed from the circulation mostly by the spleen and part of them were trapped in the lung and the small intestine. The remaining platelets retained their functional integrity. The loss of circulating platelets is manifested by the prolongation of rat tail bleeding time and is one of the factors participating in the haemostatic disturbances during anaphylaxis.

Activation and consumption of Hageman factor in the anaphylactic shock of the rat.

In the early stages of anaphylactic shock of rats pretreated with Bordetella pertussis vaccine, a prompt and parallel activation of the factor XIIa-dependent intrinsic coagulation, kinin generation, and fibrinolytic acticity was observed. The coagulation studies, the similarity of anaphylactic results with those produced by a single injection of ellagic acid, and the effective inhibition of the anaphylactic and the ellagic acid-induced activation of these pathways by lysozyme all suggest that factor XII itself becomes activated in rat anaphylaxis. As the reaction proceeded, considerable anticoagulant activities emerged, but the bradykinin and the plasminogen activator levels even further increased. During the first 10 min of anaphylactic shock, factor XII was partly consumed and this was prevented by epsilon-aminocaproic acid infusion. The results show that in pathological conditions such as anaphylaxis there is an intimate in vivo interaction among the three factor XIIa-dependent pathways.