Denise Mouton

A Major Role of the Macrophage in Quantitative Genetic Regulation of Immunoresponsiveness and Antiinfectious Immunity

Publisher Summary It is clear today that the immune system is constituted by a coordinated network of perfectly integrated and interacting cells and molecules subject to strict cooperation to ensure the highest possible efficiency in antiinfectious immunity. A simplified scheme of the immune system in higher vertebrates is represented in this chapter. The enzyme equipment of macrophage phagosomes endows these cells with bactericidal or bacteriostatic activity on ingested microorganisms, therefore, constituting the first important mechanism in antiinfectious defense. The metabolic activity of macrophages on engulfed antigens also regulates the specific response of T and B lymphocytes through a complex process of antigen handling and antigen presentation, establishing a sort of symbiotic relationship between lymphocytes and macrophages. There are two essential components in the immune response: one is specific and the other nonspecific. The specific response involves the stereospecific selective recognition. The nonspecific aspect of the immune response includes the handling of the phagocytized antigen and the rate at which the process of multiplication and differentiation of small lymphocytes takes place. The protective effect of specific vaccination is essentially based on immunological memory. The antibody molecules, according to their isotypes, play specialized defensive roles against various types of invading microorganisms, particularly in collaboration with the complement system, inducing bactericidal or opsonizing effects.

Innate resistance to infection by intracellular bacterial pathogens differs in mice selected for maximal or minimal acute inflammatory response

The intensity of nonspecific immune reaction and the host resistance to facultative intracellular pathogens are found to be associated in lines of mice selected for maximal (AIRmax) or minimal (AIRmin) acute inflammatory reactivity. AIRmax are more resistant than AIRmin mice to Salmonella typhimurium and Listeria monocytogenes infection, the differences between lines in LD50 being > 1000 and 100 times, respectively. This difference was shown to be related to the initial bacterial containment at the infectious focus, and to the control of bacterial multiplication in the spleen during the 1st week after s.  c. inoculation of the bacteria. Specific immune responses were not deeply affected by the selective process: antibody production and delayed‐type hypersensitivity were both of similar intensity in AIRmax and AIRmin mice. The differential susceptibility to infection seems independent of the Nramp‐1 locus polymorphism; therefore, these two lines represent a powerful model for investigating the role of other genetic loci regulating the nonspecific immunity effectors in the course of infectious diseases.

Genetic control of immune responsiveness, aging and tumor incidence.

Age-related alterations of the immune system affect both antibody and cell-mediated immune responses, T-cell responses being more severely affected than B-cell responses. Within the T-cell population, aging leads to replacement of virgin by memory cells and to accumulation of cells with signal transduction defects. Changes in T-cell subsets and in cytokine production profiles may produce suitable conditions for T-cell-mediated disregulation of antibody responses characterized by the production of low affinity and self-reactive antibodies. Also B-cells exhibit intrinsic defects and natural killer (NK) cell activity a profound loss in old mice. Whether age-related immune disfunctions influence life span and tumor incidence has been examined in mice genetically selected for high or low antibody responsiveness. It has been found that genetic selection of vigorous antibody responses in most cases produces mice with longer life span and lower lymphoma incidence. Moreover, the results of genetic segregation experiments indicate that antibody responsiveness and life span are polygenic traits regulated by a small number of the same or closely linked loci. Mice genetically selected for high or low mitotic responsiveness to PHA exhibit low or high tumor incidence, respectively, but no difference in life span, suggesting that T-cell activity is restricted to immune surveillance of neoplastic transformation. Studies on mice genetically selected for resistance or sensitivity to chemical carcinogenesis have uncovered loci that control both resistance to tumor induction and longevity while have no effects on immunity and disease incidence. Thus, the relative role of the immune system in conditioning the duration and the biological quality of life remains to be determined.

H-2 typing of mice genetically selected for high or low antibody production.

H and L inbred mouse strains were derived from animals selected respectively for the production of high and low titers of agglutinins against xenogeneic erythrocytes. L was found to beH-2 s . H was found to beH-2K d ,D q , with anI region derived from another (probably unknown) haplotype.

Genetics of chemical carcinogenesis: analysis of bidirectional selective breeding inducing maximal resistance or maximal susceptibility to 2-stage skin tumorigenesis in the mouse.

We report on bidirectional selective breeding, initiated from a genetically defined foundation population and carried out to selection limit, for producing lines of mice endowed with maximal resistance (Car‐R) or maximal susceptibility (Car‐S) to 2‐stage skin tumorigenesis. The initial population resulted from a balanced intercrossing of 8 inbred strains of mice. The tumors, induced by a single application of DMBA (initiation) and twice weekly applications of TPA (promotion), were benign papillomas; their number at the end of the promotion period was the phenotype chosen for assortative mating. Afterward, the majority of them regressed while others progressed to malignant carcinomas. The Car‐R line was selected through a strong challenge, while the Car‐S line selection was based on responses to decreasing concentrations of DMBA and TPA. The selection limit was reached after 14 or 15 generations showing progressive interline divergence, which strongly suggests the interaction of several quantitative trait loci (QTL). The phenotypic difference was extremely large: the tumor response was 73 times higher in Car‐S than in Car‐R mice, though the applied concentrations of DMBA and TPA were 100 and 40 times lower, respectively. The mean heritability realized during the selective breeding was 0.20 in Car‐R and 0.49 in Car‐S. Our results are compatible with a minimal QTL estimate of 8 in the Car‐R line and of 9 or 10 in the Car‐S line. The Car‐S line is also much more susceptible to carcinoma induction. An association of coat color with tumorigenesis was observed in interline F2 segregants. The Car‐R and Car‐S lines, obtained through a long‐lasting breeding program, are a unique model for identifying the QTL involved in chemical tumorigenesis and will be provided to interested investigators. Int. J. Cancer 88:424–431, 2000.

Polygenic control of quantitative antibody responsiveness: restrictions of the multispecific effect related to the selection antigen.

Among the differences observed between the various high (H) and low (L) antibody responder lines of mice resulting from distinct bidirectional selective breedings, one of the most puzzling is the variation in the “multispecific effect,” i. e., in the modification of antibody responses to antigens unrelated to those used during the selection. The best examples are the H and L lines of selection IV, selected on the basis of responses to somatic antigen of Salmonella which do not differ in their antibody responses to sheep erythrocytes (SE). However, a wide range of variability is observed in the responses of (HIV x LIV)F2 hybrids to this antigen, and it was therefore hypothesized that distinct groups of genes might regulate antibody responses to SE and the somatic antigen. Indeed, a new selection (IV-A) for anti-SE responsiveness started from these (HIV x LIV)F2 successfully produced a high and a low anti-SE responder line. The results of selection IV-A and the variance analysis of (HIV-A × LIV-A)F2 hybrids are reported. They are roughly similar to those in selection I, also carried out for anti-SE responsiveness. In vivo attempts to identify the major regulatory mechanism which contributes to the interline difference indicate that the efficiency of macrophage accessory function has been modified in selection IV-A, as was observed in selection I, whereas this function did not differ in Hév and Lév lines. Probably in relation to the involvement of macrophage function there is a notable increase of the multispecific effect in selection IV-A when compared with selection IV. The results of selection IV-A demonstrate that responsiveness to heterologous erythrocytes and to somatic antigen of Salmonella are under separate polygenic control operating through distinct regulatory mechanisms. The choice of the selection antigen and immunization procedure is of major importance for defining the gene interaction operating in each selective breeding experiment and the extent of its multispecific effect.

Basal immunoglobulin serum concentration and isotype distribution in relation to the polygenic control of antibody responsiveness in mice

Serum Ig concentration and isotype distribution were determined in the high (H) and low (L) responder lines selected for antibody response to complex immunogens. Data were recorded in normal and postimmunization sera from the H and L lines produced by five independent selective breedings (selections I, 11, III, IV, and V). Ig levels were much higher in H than in L mice of all the selections. In four selections this interline difference increased further after immunization with the selection antigens. This is in agreement with the general effect of the polygenic control of antibody responses operating in H and L lines. The Ig isotype profiles of normal sera were different in each line; however, similitudes were noticed between H and L lines in selections I and If. In contrast, in selections III, IV, and V a similar interline difference was observed: the lack of IgG2a isotype in L lines only. After immunization there were minor alterations of the isotype profiles except in the H lines of selections III and IV, in which a clear inverse modification of IgG1 and IgG2a proportions occurred. The characteristic pattern of each selection may be partially dependent on isotype-restricted regulatory effects in relation to the immunization procedure used for selective breeding.

GENETIC PARAMETERS OF THE POLYGENIC REGULATION OF ANTIBODY RESPONSIVENESS TO FLAGELLAR AND SOMATIC ANTIGENS OF SALMONELLAE

Selective breedings of mice were carried out for quantitative antibody responsiveness to flagellar Ag., f (Selection III) or somatic Ag., s (Selection IV) of two non cross‐reaction Salmonellae (Salm. tm., Salm. or.) alternated for immunization of consecutive generations. At the selection limit, these selections produced homozygous high (H) and low (L) responder lines for the character investigated: peak agglutinin response to optimal secondary immunization. The responsiveness to both f and s Ags. is submitted to polygenic regulation. The heritability (h2) realized during the selective breeding was 0.37 ± 0.07 for the response to f Ag. and 0.40 ± 0.1 for the response to s Ag. The respective part of genetic and environmental variance in F2 hybrids was 64% and 36% in selection III and 61% and 39% in selection IV. In the two selections, the dominance variance is negligible (<1%), therefore the genetic variance is essentially additive. The additive variance calculated as the heritable fraction of the F2 hybrid variance is somewhat lower, the reason for this difference is discussed. The quantitative antibody response to f Ag. in selection III is controlled by about seven independent loci. The antibody response to s Ag. in selection IV is controlled by about four independent loci. A possible association of relevant genes with the H‐2 locus was investigated. In selection III, no significant participation of H‐2 linked genes, in the regulation of responses to f and s Ags. of Salm, tm and Salm. or. could be demonstrated. In selection IV a partial contribution of H‐2 linked genes was observed concerning responsiveness to both f and s Ags. of Salm. tm.. but not to Salm. or. Ags. The H‐2 effect accounts for 25% of the total interline difference.

Multigenic control of specific and non-specific immunity in mice. A review

Abstract Anti-infectious immunity is the main component in host-resistance, and the basis of vaccination efficacy. The lines of mice selected for high or low (H or L) immune responsiveness, in which opposite extreme potentialities have been clearly defined, offer an appropriate model for investigating the genetic factors of resistance to infections. In fact, post-immunization antibody titers happen to be more than 200 times higher in H than in L antibody responder mice, whatever the antigen specificity. This is owing to the additive effect of genes located at about 10 loci, one of which is the MHC. Innate resistance to intracellular pathogens is higher in L than in H mice, owing to the differences in the macrophages activity within the two lines: antigen catabolism is faster in L macrophages, which also prove more efficient in controlling early bacterial growth. The fact that these two functions are under a common genetic regulation has recently been brought to light. As was expected, H mice have a stronger innate and acquired resistance to all the infections that can be cleared by means of antibody production. Differences between H and L mice for innate and acquired immunity are quantitative, that is: time- and dose-dependent. The alternative advantages of H or L phenotype are discussed, as regards efficacy of the immune system in natural populations, and may stand for the persistence of polymorphism at loci endowed with high selective value.

Evidence for distinct polygenic regulation of antibody responses to some unrelated antigens in lines of mice selected for high or low antibody responses to somatic antigen of Salmonella

The effect of the selective breeding of mice for high or low antibody production to complex immunogens is largely “nonspecific”, since it modifies the responsiveness of high (H) and low (L) lines to many antigens unrelated to the selection antigen. However, the nonspecific effect of the polygenic control operating in these lines is not a general feature. For example, the group of genes in selection IV, carried out for responsiveness to somatic antigen of Salmonella, does not modify the responses to sheep erythrocytes (SE). Despite equivalent responses in H and L mice of selection IV, a large variability was found in individual responses of F2 interline hybrids, which demonstrates the presence of alleles with high or low effect on responses to SE. A selective breeding (Selection IV-A) was therefore initiated from this F2 population for responsiveness to SE. A progressive interline divergence occurred during the first seven generations of selection; the interline separation was due to polygenic regulation (about four independent loci from a preliminary estimate).Equivalent responses to the s antigen of Salmonella are observed in the two lines. This constitutes additional evidence for distinct polygenic regulation of responses to SE and to somatic antigen. Moreover, the pattern of responses to several unrelated antigens (nonspecific effect) also differs between Selections IV and IV-A.