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Title: Cellular immune responses to histocompatibility antigens in the rat
Author: Chisholm, P. M.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1978
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This project was concerned with, certain immune responses mediated by T lymphocytes against major histocompatibility antigens of the rat. A cytotoxic population of lymph node calls was raised by grafting allogeneic skin and removing the draining lymph nodes eight days later. Those cells were incubated on a monolayer of allogeneic lymphocytes which had been finely attached to a polystyrene Petri dish pro-treated with poly-l-lyeino. The immune cells were physically separated into a major non-adherent fraction and a minor adherent fraction. Most of the latter could be removed for testing with an EDTA solution. In confirmation of other work, it was found that the non-adherent fraction was selectively depleted of cytotoxic activity; moreover the adherent fraction was selectively enriched for this activity. The antigenic specificity of the separation was confirmed by using monolayars of lymphocytes from different inbred strains. Unexpectedly, the small number of lymph node cells adherent to a third-party alloantigen were significantly less cytotoxic than the starting population. The main point of the work was to measure, as precisely as possible, the graft-versus-host (GvH) activity of the adherent and non-adherent cell populations in order to determine whether GvH activity was partitioned in the same way, as was cytotoxic activity. Simultaneous measurements of the two T cell activities produced decisive and were within the limits of detection, there was no partition of GvH activity, since the adherent cells, the non-adherent cells and the starting population were all precisely equal in this respect. The simplest explanation for these results requires three assumptions: (a) In an immune population GvH reactive cells and cytotoxic calls belong to separate subsets; (b) Although GvH reactive cells display surface receptors for alloantigens, these are not able to bring about partition in the in vitro system described here; (c) The cytotoxic and GvH reactive cells do not interact in the functional tests. These assumptions were generally supported, but not definitely proved, by a number of supplementary experiments including' measurement of GvH activity against 'third-party' alloantigens. The GvH activity of nonimmune lymph node cells was also identical in the adherent and nonadherent subpopulations. A radioisotopic labeling method, which has been used to estimate the proportion of T cells responding to a given major alloantigen complex in a systemic GvH reaction, was modified in order to estimate the proportion of immune cells which adhered to allogenic monolayers as a consequence of antigen recognition. A population of cells which had been immunised against one major alloantigen was labelled with either 3H- or 14C-uridine, and a population immune against a third-party alloantigen was labelled with the alternative isotope. The ratio of 3H to 14C in the adherent fraction, particularly that subfraction which was eluted with EDTA, always reflected the increased binding of the homologous immune population. On average, approximately 3% of the uridine-labelled coils were specifically adherent. This is of the same order as estimates of the proportion of cytotoxic cells in immune populations. However, when similar ?? were performed with immune populations labelled in vitro, with .7 H- or 14C thymidino, it was found that, on average, 2 of the MA nynthocising population was specifically adherent. This suggests that most of the specifically adherent cells belong to the actively proliferating population, which others have shown to include most of the cytotoxic activity at this stage of the response. Nevertheless, the prooiso relationship between specific adherence in vitro, and cytotoxicity has not boon determined. Several explanations are considered for the in vitro observation that cytotoxic T cells selectively adhere to the appropriate antigens while GvH reactive cells do not. The individual receptors for antigen may have higher affinity or, alternatively, the cytotoxic cell may have higher avidity because it has a greater density of receptors. A third explanation is that the cytotoxic cell reacts to the engagement of its receptors by a non-specific increase in its adhesiveness. The only possibility which these experiments rule out is that the cytotoxic cell is more adherent before encountering antigen and that antigen-specific binding adds to this to make the total adherence to allogenic cells greater than is the case with GvH reactive cells.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available