The functional significance of polymorphism among MHC class II promoters in man and mouse is here reviewed, mainly in terms of the hypothesis of differential expression. The hypothesis proposes that ...differences between antigen-presenting cells in MHC class II expression exert a co-dominant effect on the Th1-Th2 cytokine balance, such that class II molecules of one type come to control to a greater extent the production of one group of cytokines, and those of another type the production of the alternative group. The survey deals with the influence of signal strength and antigen-presenting cell type on T-cell subset differentiation; functional differences between MHC class II molecules not obviously related to determinant selection; disease protection mediated by HLA alleles; mechanisms possibly responsible for allotypic and isotypic bias; overdominance (heterozygous advantage) in selection for expression of class II alleles; MHC class II promoter structure and function; inter-locus and inter-allele variability within human MHC class II gene upstream regulatory regions; a comparison of these polymorphisms in mouse and man; read-out of class II promoter function; and a comparison with expression of MHC class I. We conclude that the evidence that this variation is functionally active (i.e. controls expression) is increasing, but is not yet compelling. The crucial test still to come, we suggest, is whether or not the biological effects attributable to this polymorphism will line up with molecular studies on expression.
Expression of HLA and CD1b molecules was investigated in the THP‐1 macrophage cell line within 2 weeks following phagocytosis of mycobacteria or Escherichia coli. During the first 2 – 3 days, cell ...surface expression of HLA class II and CD1b was drastically down‐modulated, whereas HLA class I expression was up‐modulated. In the following days both HLA class II and CD1b expression first returned to normal, then increased and finally returned to normal with kinetics similar to that observed for the steadily increased HLA class I. The initial down‐modulation of HLA class II and CD1b cell surface antigens was absolutely dependent on phagocytosis of bacteria. Further studies indicated that initial HLA class II cell surface down‐modulation (1) was not due to reduced transcription or biosynthesis of mature HLA class II heterodimers, (2) was only partially, if at all, rescued by treatment with IFN‐γ, although both mRNA and corresponding intracellular proteins increased up to sixfold with respect to untreated cells, and (3) resulted in failure of THP‐1 cells to process and present mycobacterial antigens to HLA‐DR‐restricted antigen‐specific T cell lines. The existence of a transient block of transport of mature HLA class II heterodimers to the cell surface in the first days after phagocytosis of bacteria may have negative and positive consequences: it decreases APC function early but it may increase it later by favoring optimal loading of bacterial antigens in cellular compartments at high concentration of antigen‐presenting molecules.
Major histocompatibility complex class II molecules (MHC-II) are highly polymorphic cell surface glycoproteins composed of a 34-kDa alpha chain and a 28-kDa beta chain which play a fundamental role ...in the homeostasis of the immune system. In man, three functional class II heterodimers are expressed on the cell surface: HLA-DR, DQ, and DP. In mouse, only two molecular subsets have been described, namely, I-A and I-E. MHC-II act as receptors for antigenic peptides that can be recognized by the clonotypically distributed T-cell receptor (TCR) and trigger the cascade of events leading to a normal immune response. This `MHC-restricted' recognition of antigen by T cells is the final result of a developmentally regulated process taking place mostly in the thymus, where T cells learn to recognize self antigens presented by MHC class II molecules particularly expressed on thymic epithelial cells (TECs). It is generally believed that during the maturation process, T cells expressing TCRs with high affinity for self MHC-antigen are negatively selected and die. As a consequence, only the T cells with low affinity TCRs are allowed to leave the thymus and to colonize the periphery. Thus, the expression of MHC class II molecules is fundamental for modelling the T-cell repertoire, for the acquisition of tolerance, and for recognition of antigen. The expression of MHC class II antigens is a highly regulated, developmentally controlled process. On differentiated cells, class II antigens are expressed only on a few cell types, mainly confined to, or in strong contact with, the immune system as is the case of B cells, macrophages, and TECs. Moreover, the mode of expression of class II antigens is distinct in the various cell types. B cells express class II molecules constitutively, whereas macrophages and TECs express them after induction with a variety of stimuli, among which the cytokine IFN- gamma is certainly one of prominent biological relevance. This developmentally and functionally controlled expression of class II molecules is mainly regulated at the transcriptional level. Many studies have demonstrated that this is basically true for both constitutive and inducible expression.
. The growth kinetics of 9L (rat glioblastoma cell line) and U118 (human glioblastoma cell line) multicellular tumour spheroids (MTS) have been investigated by non‐linear least square fitting of ...individual growth curves with the Gompertz growth equation and power spectrum analysis of residuals. Residuals were not randomly distributed around calculated growth trajectories. At least one main frequency was found for all analysed MTS growth curves, demonstrating the existence of time‐dependent periodic fluctuations of MTS volume dimensions. Similar periodic oscillations of MTS volume dimensions were also observed for MTS generated using cloned 9L cells. However, we found significant differences in the growth kinetics of MTS obtained with polyclonal cells. Our findings demonstrate that the growth patterns of three‐dimensional tumour cell cultures are more complex than has been previously predicted using traditional continuous growth models.
Qualitative and/or quantitative alterations in the expression of the MHC class II molecules affect the onset and maintenance of the immune response and may be the basis of a wide variety of disease ...states, such as autoimmunity and immunodeficiency.
CIITA is a major physiological regulator of the expression of MHC class II genes. The availability of CIITA ap- pears generally essential for MHC class II gene expression, and hence its own transcriptional regulatory mechanisms result of fundamental importance for a correct homeostasis of the immune response. Therefore, it is possible to hypothesize that variability at the CIITA-encoding locus,
AIR-1, could constitute an additional source of susceptible traits to autoimmune diseases. Mutations at
AIR-1/CIITA promoters could modulate expression of CIITA. Variations in CIITA expression could influence the qualitative and quantitative expression of MHC class II molecules at cell surface. We have analyzed sequence variation at
AIR-1/CIITA promoters by PCR-SSCP in 23 IDDM and 30 RA patients compared to a sample of 19 unaffected normal controls and 16 unaffected IDDM family members, for a total of 88 Caucasian subjects from the Northeast of Italy. No sequence difference was found at the four
AIR-1/CIITA promoters between autoimmune patients and normal controls. Moreover, the promoters resulted invariant within the entire group of 88 subjects analyzed, comprising patients and controls. This finding suggests a possible selective advantage in maintaining CIITA upstream regulatory sequences invariant.
It is generally believed that the various MHC class II molecules are expressed coordinately in B cells. To investigate this aspect in more detail, interspecies somatic cell hybrids were constructed ...between Raji or RJ 2.2.5 (a class II-negative derivative of Raji) human B cells and M12.4.1 mouse B cells. In both types of hybrids, HLA-DR and -DP, but not -DQ, molecules were expressed at the cell surface. The specific lack of expression of DQ Ags correlated with undetectability of newly synthesized DQ alpha beta heterodimers, as assessed by biosynthetic labeling and immunoprecipitation with a variety of DQ-specific mAbs. Studies at the mRNA level showed that apparently normal DQ alpha and DQ beta transcripts were present in the hybrids at levels comparable, if not higher, with the levels of DR- and DP-specific transcripts. From these results, we conclude that lack of appreciable amount of DQ molecules in the hybrids is caused by a post-transcriptional block. To date, these findings represent a rather unique example of noncoordinate expression of MHC class II Ags caused by distinct post-transcriptional mechanisms. These data may be relevant to a more correct interpretation of the functional role of the various MHC class II molecules, particularly with regard to the well-known association of HLA-DQ with many autoimmune diseases. Possible mechanisms at the basis of the distinct control of expression within the MHC class II molecular pool are discussed.
The favorable results obtained by other authors with polichemotherapy encouraged us to employ therapeutic scheme using a combination of 4 drugs. Treatment envolved the administration of 300 mg/mz ...cyclophosphamide, 350 mg/m2 5-fluorouracil, 10 mg/mw2 methotrexate i.v. on alternate days 6-8 times, and 15 mg bleomycin on alternate days until a total dose of 150-200 mg is reached. Thirty-five out of 37 patients treated with this protocol (30 previously treated and 5 not) qualified for analysis; the site of the neoplasm, mostly squamous cell carcinoma, was different; for the most part it was in the larynx (18/35) and the oral cavity (10/35). Complete remission was achieved in 9/35 patients (25.7%), varying from 5 to 33 months (median 22); partial remission was achieved in 15/35 cases (42.8%), varying from 1 to 14 months (median 3); and there was no success in 11/35 cases (31.5%). Overall, a total remission greater than 50% was observed in 24/35 patients (68.5%). The most serious side effects both ascribed to BLM were observed in the central nervous system (increasing drowsiness and coma) and the lung. This study has shown that in the ultra head and neck malignancies medical treatment can achieve satisfactory results.
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