Histological changes in the epithelium of the small intestine during protein absorption in the new-born animal

Transmission of antibodies from mother to young: Evolutionary strategies in a proteolytic environment

Transmission of antibody from mother to young is an essential process. Maternal proteins provide both food (if digested) and immune protection (undigested antibody) for the offspring. The processes for transfer changed and diversified during vertebrate evolution, using receptor-dependent and -independent mechanisms pre- and postnatally. Transmission frequently proceeds in a proteolytic environment and different mechanisms evolved for the protection of antibody. The present review focuses on the relationship of acquisition of passive immunity to other physiological processes.

Ultracentrifuge and electrophoretic studies on the proteinuria of the new-born calf

1. Many immunologically related components occur in bovine serum and colostrum, but certain components in each are absent in the other (specific components). Two components (or groups) occur in colostrum which do not appear in serum, and these can be associated with electrophoretically slow and fast colostrum components.

2. Pre-colostral and adult urines contain low concentrations (<0·2 g./ 100 ml.) of protein which, though immunologically related to serum proteins, does not closely resemble any major serum component in physical properties.

3. Urines collected during the period of proteinuria contain increased concentrations of protein (up to 2 g./ 100 ml.) which is immunologically related to both serum and colostrum. From the presence of material related to specific colostrum components (and the absence of specific serum components), the added protein evidently originates from colostrum rather than serum. The total added protein possesses components with electrophoretic mobilities covering a wide range, with appreciable protein faster than albumin at pH 8. From sedimentation studies, the added proteins resemble the slower sedimenting colostrum proteins (β-lactoglobulin and lactalbumin) and contain no observable material with the sedimentation behaviour of immune lactoglobulin.

4. Immunologically, the added protein is related only to the electrophoretically faster of the specific colostrum components, and this applies also to post-colostral lymph in spite of its very high content of immune lactoglobulin. It follows that the specific electrophoretically slower colostrum components represent only a small proportion of the total immune lactoglobulin fraction.

5. The presence in urine, collected during the period of proteinuria, of antibody activity (deriving originally from the calf's mother), and of protein with the approximate electrophoretic mobility of, but without the sedimentation behaviour of γ-globulin, is to be explained probably on the basis of molecular degradation at some stage between absorption from the intestine and excretion in the urine.

6. The low molecular weight colostrum components, though present in low concentration in the lymph, are absent or below the detectable threshold in post-colostral sera (containing much material derived from immune lactoglobulin), and this is thought to be partly due to selective action by the kidney, allowing the passage of, and causing concentration of low molecular weight protein in the urine, whilst retaining higher molecular weight protein in the serum.

7. The results show that the proteinuria of the new-born calf arose mainly from low molecular weight protein in the colostrum which was absorbed from the gut together with the immune lactoglobulin. Owing to the small molecular weight, this, the former protein, was subsequently cleared from the circulation probably by glomerular filtration, accounting for the difficulty of detecting them electrophoretically and ultracentrifugally. On the other hand, the immune lactoglobulin with its much higher molecular weight was not so cleared from the circulation and is readily detected there.

The authors wish to thank Sir Alan Drury, F.R.S., for his support during the course of this work, Mr N. Buttress and Mr D. Hardman for technical assistance and Mr J. Clark for assistance in the care and handling of the calves.

Ultrastructure of pre- and postcolostral enterocytes of the newborn calf

Ten calves were used to elucidate the ultrastructure of enterocytes before and 24 h after colostral intake. Tissue samples were obtained from duodenum, jejunum (5 locations) and ileum. Protein A-gold technique was applied to immunoelectron-microscopically demonstrate colostral IgA. The prominent feature of the precolostral enterocytes are intracytoplasmic vacuoles. The frequency of vacuoles increases from cranial jejunum to ileum and from the villi bases to the tips. The appearance of absorptive vacuoles after colostral administration correlates with the incidence of precolostral empty vacuoles. Bovine IgA was detected in absorptive vacuoles and within the intestinal lumen of postcolostral calves. In addition to a diffuse IgA labelling of most vacuoles, a few corresponding enterocytic vacuoles labelled inhomogenously or negatively. This study demonstrates morphologically that the main site of colostral absorption is the middle-to-caudal region of the small intestine. Immunoelectron microscopy of IgA labelling provides indications of a selective IgA absorption in addition to pinocytosis.

Endogenous production of immunoglobulin IgG1 in newborn calves

There is a decrease in the specific activity of labeled IgG1 of serum over 3 wk following the feeding of iodine-125 labeled immunoglobulin IgG1 in colostrum to calves at birth. This decrease indicated the appearance of new IgG1 from some source. To determine if this new IgG1 came from endogenous production in the calf or from continued small amount of intestinal absorption from milk, labeled IgG1 was added to normal milk and fed to calves of various ages up to 3 wk after an initial feeding of colostrum at birth. Labeled IgG1 was also added to colostrum fed to calves at birth, and the calves were maintained on a normal milk diet or fed a synthetic milk diet. Determination of iodine-125 in the serum protein fractions of these calves indicated that there was no apparent intestinal absorption of labeled IgG1 from the milk in the period from 2 days to 3 wk. Furthermore, comparable decreases occurred in the specific activity of labeled IgG1 in serum in the calves fed the labeled IgG1 in colostrum at birth and subsequently maintained either on a diet including milk or on the synthetic milk diet devoid of IgG1. The results support the conclusion that the origin of new IgG1 in the calf after about 36 h and up to about 3 wk of age arises from endogenous production at a rate of about 1 g of IgG1 per day.

The use of [125-I] polyvinyl pyrrolidone K. 60 in the quantitative assessment of the uptake of macromolecular substances by the intestine of the young rat

1. A method has been developed which allows the quantitative estimation of the uptake of labelled polyvinyl pyrrolidone (PVP) of mean mol. wt. 160,000 (K. 60) by the wall of the small intestine of young rats.2. Four hours after feeding a standard dose of [(125)I]PVP by stomach tube, the small intestine was thoroughly washed out, and the radioactivity of the intestinal wall measured. Under these conditions, the small intestine of animals less than 18 days old took up more than 50% of the radioactivity which had left the stomach. There was no increase in PVP uptake if the duration of absorption exceeded 4 hr. The PVP was taken up by the epithelial cells of the villus, and its intracellular localization has been demonstrated by fluorescence microscopy and can be related to vacuolation in the cells.3. In animals between 18 and 20 days old the uptake of PVP declined progressively, until, in animals more than 20 days old, less than 5% of the radioactivity was taken up by the intestinal wall.4. There is good agreement between the reported age of termination of antibody absorption in young rats and the age at which PVP uptake ceased in the present experiments. It is suggested that the loss of ability of the intestine to take up substances of high mol. wt. may be the factor which limits the duration of the period of antibody absorption in this species.

Electrophoretic and immunological studies on sera from calves from birth to weaning. II. Electrophoretic and serological studies with special reference to the normal and induced agglutinins to Trichomonas foetus

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Passively and actively acquired antibodies for Trichomonas foetus in very young calves

1. The normal agglutinin (n.a.) forTrichomonas foetusfound in all normal adult cattle has a titre of 1:48 to 1:96. N.a. appears to be specific forT. foetusand cannot be absorbed by other flagellates such asT. vaginalisor even completely by the heterologous serological variety ofT. foetusitself. The n.a. appears to be a native constituent of the serum and not to be induced by an exogenous antigen.

2. The n.a. passes into the serum of the calf from the maternal colostrum during the first 24 hr. of life. The elimination of the passive n.a. and the development of the autogenous newly formed n.a. in the calf are traced. The passive n.a. disappeared from the 17th to the 55th day and the autogenous n.a. began to appear as a rule from the 35th to the 60th day and was fully established by the 63rd to the 113th day.

3. The elimination of the maternal, induced antibody acquired passively from the colostrum took place logarithmically. The rate measured by the half-life ranged from 14 to 20 days, but in one animal which took a very large amount of colostrum it was 57 days.

4. The intramuscular injection ofT. foetusantigen into very young calves up to 4 weeks old induced no antibody. When the doses were relatively small the animal produced antibody to antigen given at a later period. When a very large amount was injected in this early period the subsequent capacity to respond to the same antigen but not to other antigens was seriously impaired.

The personal encouragement of Prof. H. G. Lamont and the support afforded by the Ministry of Agriculture, Northern Ireland, are gratefully acknowledged.