The differential effect of hydrocortisone on the short-lived small lymphocyte

Effect of alternate-day hydrocortisone therapy on the immunologically immature rat. I: Effect on blood cell count, immunoglobulin concentrations, and body and organ weights

The effect of 400 mg/M2/day of hydrocortisone, given alternatively from day 7 to day 19, was studied in the immunologically immature rat, a steroid-sensitive species. Animals, sacrificed 2 days following the completion of treatment, suffered from an underweight thymus and spleen, leucocytosis, and peripheral lymphocytopenia, probably not due to redistribution of lymphocytes from blood to tissues. In addition, a significant decrease in serum IgM concentration, reflecting a deficit in primary immune response, was evidenced. Although the percentage of lymphocytes returned to normal in rats sacrificed 23 days after treatment, an overweight thymus and spleen and persistent leucocytosis may reflect a compensatory overactivity of the developing immune system. In contrast, serum IgM concentration increased, but to a value less than normal. An indirect effect of hydrocortisone on lymphocytes through its action on thymus, as well as a direct effect on B cells, is suggested. Unlike humans, alternate-day steroid therapy delayed the normal growth pattern of rat, with a defective rate of growth only during the treatment period.

Effect of alternate-day hydrocortisone therapy on the immunologically immature rat. II: Changes in T- and B-cell areas in spleen

The histologic effect of 400 mg/M2/day of hydrocortisone, given alternatively from day 7 to day 19 after birth, was studied on the spleen of the immunologically immature rat. Two days after the cessation of treatment, the periarteriolar lymphatic sheaths were found to be largely depleted of small lymphocytes. Immunoperoxidase studies confirmed a depletion of T lymphocytes. The effects of hydrocortisone on the thymus seem to be more important than its direct lymphocytolytic effect in producing this splenic lesion. In contrast, no apparent change in the number of medium-sized B lymphocytes in the marginal zone was detected. Medium-sized B lymphocytes of the spleen, reported to be responsible for IgM synthesis, appeared to be subjected to a different mechanism of hydrocortisone action, other than lysis, resulting in a decrease in antibody production. Primary follicles were not seen in spleens of hydrocortisone-treated rats. Twenty-three days after treatment, spleens had a histologically normal appearance.

Immune suppression and histophysiology of the immune response. I. Cortisone acetate and lymphoid cell migration

Seven daily intramuscular (im) injections of cortisone acetate (25 mg/Kg b.w.) given to rats or rabbits produced, (i) a pronounced reduction in the numbers of small lymphocytes in thymus-independent areas, (ii) atrophy of the thymic cortex, (iii) atrophy of germinal centres and (iv) a consequent depressed production of germinal centre-derived cells. Lymphocyte depletion was not caused by cell lysis. Moreover cell traffic between peripheral lymphoid organs did not seem to be altered. A revival of the depressed germinal centres in cortisone-treated (inbred) rats could be achieved by a transfer of bone-marrow cell suspensions from normal, cortisone-treated or T-cell-deprived animals. It was concluded that cortisone acetate arrests the migration of B-lymphocytes from the bone marrow to germinal centres in peripheral lymphoid organs, and that the accumulations of lymphoid cells in the bone marrow of cortison-treated animals might be composed of immature or mature T- and B-lymphocytes.

Short time observations of morphological changes and cholinesterase distribution in lymphatic organs of the mouse after corticosteroid and X-ray treatment

The changes in thymus, spleen and lymph nodes of the mouse after a single cortisone application or a single whole body x-irradiation were investigated morphologically and histochemically. During 24 h the alterations following the cortisone application are at all stages examined indistinguishable from those following the x-irradiation. The first signs of lymphocyte destruction can be observed already in the first two hours after treatment. Almost at the same time macrophages accumulate at the sites of cell death in the lymphatic organs studied. The eosinophils display a different behaviour. While they accompany the macrophages in the thymus already at the first stages, they appear in the spleen and lymph nodes with a latency of 6 and 8 h, respectively. The highest amount of necrotic cells is found ten hours after both treatments. At the same time the accumulation of macrophages and eosinophils reaches its maximum. The cholinesterase in the lymphatic organs is largely the true cholinesterase. The enzyme-activity increases in the cortex of the thymus gradually 6 h after treatment, showing the highest deposit of reaction product at 10 h. In spleen and lymph nodes the cholinesterase shows only slight variations. The possible role of the cholinesterase-activity in these non-cholinergic tissues is discussed.

Qualitative and quantitative morphologic study of Peyer's patches of the mouse after neonatal thymectomy and hydrocortisone injection

Peyer's patches in normal adult mice, neonatally thymectomized mice and mice injected with hydrocortisone were studied qualitatively and quantitatively by light microscopy. The patch was divided into germinal center, follicular area, parafollicular area and dome area. In normal mice, the volumetric ratio of the germinal center to the entire patch was 30.9%; that of the follicular area, 33.3%; that of the parafollicular area, 27.7%; and that of the dome area, 8.2%. Thymus-dependent small lymphocytes were 40% of small lymphocytes in the patch. Out of the total thymus-dependent small lymphocytes in the patch, 13% were included in the germinal center; 19%, in the follicular area; 62%, in the parafollicular area; and 6%, in the dome area. Hydrocortisone-sensitive small lymphocytes were 65% of the total small lymphocytes in the patch, the germinal center contained 9%; the follicular area, 84%; the parafollicular area, 2%; and the dome area, 5%. The epithelium over the dome area was invaded by numerous small lymphocytes. Forty-eight percent of lymphocytes within the epithelium over the dome were thymus-dependent and 67% were hydrocortisone-sensitive. It is concluded that Peyer's patch may be considered as a peripheral lymphatic tissue, functionally as well as morphologically.

Experimental allergic encephalomyelitis. Water, sodium and potassium concentration in spinal cord and hemispheres and their changes after dexamethasone treatment

Water content, Na+, K+ and Cl- concentration were measured in rats with experimentally produced allergic encephalomyelitis. Increase of water content by 10%, accumulation of Na+ by 13%, of Cl- by 20% and decrease of K+ by 10% was observed in the spinal cord, but no substantial changes were found in the brain tissue. The hydration of spinal cord is accompanied by perivascular infiltrates. Dexamethasone, administered from day 5, after injecting sensitising encephalitogenic basic protein, effects normal levels of water content and Na+, K+ and Cl- concentration.

Quantitative studies of lymphocytes and other cell populations in the bone marrow of neonatally thymectomized C3H mice

The effects of neonatal thymectomy on the development of the lymphoid, erythroid and granulocytic cell populations in mouse bone marrow have been assessed by quantitative techniques. The numbers per unit volume of bone marrow of 17 cell types were determined in neonatally thymectomized and sham thymectomized C3H mice at two, four and eight weeks of age, and compared with those of normal C3H mice. After neonatal thymectomy the numbers of small lymphocytes, large and medium-sized lymphoid cells, and erythroid cells reached normal levels at two weeks but fell progressively to 18%, 22% and 42% of normal, respectively, by eight weeks. In sham thymectomized mice these cell populations did not differ significantly from normal. Immature and mature granulocytes were elevated in numbers two weeks after either neonatal thymectomy or sham thymectomy, suggesting a transient non-specific stimulation of granulocytopoiesis. During continuous infusion of 3H-thymidine for ten days in neonatally thymectomized mice aged four weeks and eight weeks many bone marrow small lymphocytes remained unlabeled. The results demonstrate that early postnatal development of bone marrow lymphoid and erythroid cells proceeds normally in the absence of the thymus, in accord with the concept of the bone marrow as a primary site of lymphocyte production and differentiation. In addition, some slowly-renewing small lymphocytes in bone marrow appear to be thymus-independent cells.

Lymphocyte populations in mouse bone marrow: quantitative kinetic studies in young, pubertal and adult C3H mice

Continuous 3-H-thymidine infusion was used to characterize two kinetic subpopulations of small lymphocytes in mouse bone marrow during normal growth and development. Young (4 wk), pubertal (8 wk) and mature (16 wk) C3H mice were infused subcutaneously with 3-H-thymidine for periods up to 10 days. Femoral marrow was then examined in radioautographic smears. During the first 3 days the proportion of marrow small lymphocytes labelled by 3-H-thymidine showed a rapid exponential increase to 93%, 81%, and 72% in 4 wk, 8 wk and 16 wk mice respectively. The rate of appearance of labelled small lymphocytes then declined markedly but remained higher in younger than in older animals. The labelling curves were found to represent the summation of two exponential curves from which the proportions and renewal rate of corresponding cell populations were calculated. Most marrow small lymphocytes comprised a rapidly renewing population but in mice of increasing age the relative incidence of these cells fell (93-3% at 4 wk; 88-0% at 8 wk; 78-5% at 16 wk) and their half-renewal time (T1/2) lengthened (14 hr at 4 wk; 18 hr at 8 wk; 24 hr at 16 wk). The remaining small lymphocytes were slowly renewing with mean T1/2 OF 4, 7 and 14 days in 4, 8 AND 16 wk mice, RESPECTIVELY. Some heavily labelled small lymphocytes persisted in the marrow up to 10 wk after fourteen daily 3-H-thymidine injections in 10-12 wk mice. The numbers of rapidly renewing cells decreased from 604 times 10-3 to 228 times 10-3 per mm-3 of marrow from 4 wk to 16 wk, respectively, while slowly renewing cells increased from 44 times 10-3 to 61 times 10-3 per mm-3. The total number of nucleated marrow cells per femur increased from 4 wk to 16 wk but the rapidly renewing small lymphocytes per femur fell in numbers by 36% and in renewal rate by 63%. The results demonstrate a selective change in bone marrow small lymphocytes with age; rapidly renewing cells decline in number and renewal rate while the number of slowly renewing cells increases. The concept of bone marrow as a primary lymphoid organ is discussed.

The effect of in vivo hydrocortisone on subpopulations of human lymphocytes

This study was designed to determine the effect of in vivo hydrocortisone on subpopulations of lymphoid cells in normal humans. Subjects received a single intravenous dose of either 100 mg or 400 mg of hydrocortisone, and blood was drawn at hourly intervals for 6 h, and then again at 10 and 24 h after injection. Profound decreases in absolute numbers of circulating lymphocytes and monocytes occurred at 4-6 h after both 100 mg and 400 mg of hydrocortisone. Counts returned to normal by 24 h. The relative proportion of circulating thymus-derived lymphocytes as measured by the sheep red blood cell rosette assay decreased maximally by 4 h and returned to base line 24 h after hydrocortisone. There was a selective depletion of functional subpopulations of lymphocytes as represented by differential effects on in vitro stimulation with various mitogens and antigens. Phytohaemagglutinin response was relatively unaffected, while responses to concanavalin A were significantly diminished. Responses to pokeweed mitogen were unaffected by 100 mg of hydrocortisone, but greatly diminished by 400 mg of hydrocortisone. In vitro responses to the antigens streptokinase-streptodornase and tetanus toxoid were markedly diminished by in vivo hydrocortisone. Reconstitution of monocyte-depleted cultures with autologous monocytes partially corrected the diminished response to antigens. This transient selective depletion of monocytes and subsets of human lymphocytes by a single dose of hydrocortisone is most compatible with a redistribution of these cells out of the circulation into other body compartments.

A study of gluco-corticosteroid-induced pyknosis in the thymus and lymph node of the adrenalectomized rat

Pyknotic nuclei, observed in the thymus of steroid-treated rats, are dense, homogeneous, intensely basophilic and Feulgen positive. Under the electron microscope, the image is that of a complete segregation of the chromatin from the nuclear sap producing a margin or crescent of condensed chromatin. Approximately 30% of all small thymocytes appeared to undergo this type of degeneration within 3-4 hr after administration of the synthetic corticosteroid, dexamethasone. At this time, pyknotic thymocytes were observed in clusters, probably as a result of the activity of dense reticular cells and macrophages. Topographical and experimental data suggest the existence of a select population of steroid-sensitive thymic cells. Furthermore, on the basis of thymidine-(3)H incorporation studies, it appears that the steroid-sensitive population of thymocytes does not correspond to "aged" cells. In addition, many plasma cells became pyknotic after the same steroid treatment, indicating an unexpected similarity between their nuclei and those of lymphocytes. Finally, steroid failed to induce pyknosis of thymocytes in a variety of in vitro experiments, suggesting that the in vivo effect of steroid is of an indirect nature. The results are discussed in terms of (a) the nature of the nuclear changes characterizing pyknosis, (b) the hypothetical mechanism whereby steroids trigger such changes, and (c) the population of cells susceptible to steroid-induced pyknosis.