R.C. Potts

Histometric study of the localisation of lymphocyte subsets and accessory cells in human Mantoux reactions.

Intradermal injection of purified protein derivative produced typical delayed type hypersensitivity reactions in five healthy human subjects. The major subpopulations of lymphocytes and certain accessory cells were located in frozen sections of biopsies of the lesions with monoclonal antibodies and immunohistochemical staining. The densities (expressed as number/unit area for comparison) of the different types of cells were counted at various microanatomical locations in the tissue. The inflammatory cells were concentrated in narrow zones, initially (24 h) only surrounding small blood vessels but later (48-96 h) also around sweat ducts. Lymphocytes were the predominant cell type at these sites with T4 and T8 cells randomly intermixed at a ratio similar to that in the mononuclear cell fraction of the peripheral blood samples removed at the time of biopsy. There was also a scanty diffuse infiltrate in the intervening dermis, but here the T4:T8 ratio was significantly lower than that in the peripheral blood or perivascular cuffs. There was considerable intersubject variation in the relative preponderance of T8 cells in the diffuse infiltrate. The results suggest that there is no subset selection in the initial emigration of lymphocytes through vascular endothelium in the delayed hypersensitivity reaction, but that the subsets behave differently during the subsequent migration through the tissues. It remains to be determined whether the extent to which T8 cells migrate more rapidly than T4 cells through the tissues may influence the reaction at the site of entry of organisms or antigens into the body by altering the balance of the immunoregulatory lymphocyte subsets. This may underlie some of the differences in susceptibility to infection between subjects and determine the type of granuloma that develops in a particular patient.

A PASSIVE HAEMAGGLUTINATION (TRC) INHIBITOR IN THYROTOXIC SERUM

The tanned red cell haemagglutination test system is widely used in the screening of thyroid and other auto‐immune diseases. We report a phenomenon which casts some doubt on the reliability of the technique.

Early delayed hypersensitivity responses in tuberculin skin tests after heavy occupational exposure to tuberculosis

The early (six hours) reaction to tuberculin skin testing was studied in 33 Indonesian hospital workers with frequent occupational exposure to M tuberculosis and compared with responses maximal at the usual time (48 hours) in factory workers, from the same locality but with only occasional occupational exposure, to determine the nature of the early reaction. The early reaction had the same general histopathological appearance as that seen in the conventional (48 hour) reaction, and both had an infiltrate consisting largely of T lymphocytes and macrophages. The cell densities were lower in the six hour reactions, but the relative concentration of macrophages was greater in the earlier response. These histometric measurements suggested that the six hour reaction was an accelerated delayed hypersensitivity reaction. Moreover, the absence of a specific IgE response or of particulate masses of Ig or complement, made it unlikely an anaphylactoid or Arthus-type reaction could have been responsible. It is concluded that those with frequent occupational exposure to M tuberculosis have larger numbers of circulating T cells reactive with mycobacterial antigens, so that the development of the skin test response to tuberculin is less dependent on by-stander cell infiltration to mediate the delayed hypersensitivity reaction than the reactions in those with less intense and less frequent natural exposure. The skin test response maximal at six hours is probably a hyperimmune reaction to an antigen recognised by T cells.

Mechanisms by which barbiturates suppress lymphocyte responses to phytohaemagglutinin stimulation

Certain barbiturates (the intermediate- and short-acting drugs) reduce the growth of PHA-stimulated peripheral blood mononuclear cells, but phenobarbitone (a long-acting drug) is ineffective: replicative growth is more sensitive than activation. This action is associated with a marked reduction in the density of interleukin-2 receptors on the cell membrane and of the numbers of cells expressing them, but the growth rate cannot be restored by supplementation of the tissue culture medium with exogenous interleukin-2. The affected cells show swelling of the mitochondria and cytoplasmic fat globules: the presence of residual bodies and myelin figures indicate an increase in the rate of degradation of organelles. There was no appreciable increase in the number of necrotic cells seen on electron microscopy of cultures exposed to high concentrations of thiopentone or other potent barbiturates, but the presence of debris in the DNA cytogram at 72 h indicated some increase in the death rate of cells exposed to the growth suppressing barbiturates. It would be inadvisable to administer these short- and intermediate-acting barbiturates over long periods, particularly at high dosage, because of the potential danger of iatrogenic immunosuppression.

Skin test responsiveness to four new tuberculins in patients with chronic obstructive airways disease receiving short term high doses of, or long term maintenance treatment with, prednisolone: clinical appearances and histometric studies.

The response to skin testing with tuberculins extracted from various species of mycobacteria was studied in 49 patients from Dundee with chronic obstructive airways disease. Seventeen had never been treated with steroids (group 1), 17 were receiving short term high doses of prednisolone (group 2) and did not have impaired Synacthen tests; 15 were receiving long term maintenance treatment and did have impaired Synacthen tests (group 3). Erythematous and indurated reactions were seen in a few patients, more commonly to antigens from Mycobacterium tuberculosis than to the other species: neither of the latter treatment groups showed appreciable reduction in reactivity compared with that of the group 1 patients. The number and microanatomical distribution of the T4 and T8 lymphocytes and the M3 bearing monocytes and macrophages was studied immunocytochemically in cryostat sections of biopsy specimens from the antigen injection sites. The density of these cells was significantly less in clinically negative reactions than in those with erythema or induration, but was unrelated to the presence or absence of a history of treatment with prednisolone. The T4:T8 ratio in the section as a whole was similar to that of the peripheral blood, but T8 cells were relatively more common in the perivascular and periappendicular foci, and T4 lymphocytes were predominant in the diffuse component of the infiltrate. I12 receptor bearing lymphocytes were uncommon: such cells were least common in the clinically negative reactions, but the number and distribution were apparently unrelated to the presence or absence of prednisolone treatment. It was concluded that currently accepted regimens of treatment with prednisolone did not reduce the effector arm of type IV (delayed type hypersensitivity) responses and so are unlikely to compromise this aspect of protective immunity.