The birth of immunology. III. The fate of the phagocytosis theory.

During the period of 1895-1910, immunology was preoccupied with defining the cellular (Elie Metchnikoff's phagocytosis theory) as opposed to the humoral basis of bactericidal defense. Although initial discovery of immunopathologic phenomena had been made (e.g., relating to transplantation, autoimmunity, allergy), focus on microbicidal therapy and diagnosis of infectious diseases remained the major stimuli of inquiry. The debate concerning the relative roles of phagocytes, complement, amboceptors (sensibilizing factors, antibody, antitoxins), various lysins (e.g., bacteriolysins, spermatolysins, hemolysins), agglutinins, stimulines, and then Almoth Wright's opsonins reflects the ambiguity of a scientific language being created in an era still struggling with a poorly defined experimental system, for the language, both its vocabulary (newly studied phenomena) and grammar (operational mechanisms) was yet to be codified. The joint award of the Nobel Prize to Metchnikoff and Paul Ehrlich in 1908 for their respective contributions to the "theory of immunity" appeared to proclaim a consensus, but the secret Nobel Committee reports that evaluated Metchnikoff's contributions reveal only a grudging acceptance of his position, and the award was clearly made on the basis of an apparent complementarity between the theoretical views of the humoralists and those elements of the phagocytosis theory that fit the then current discussion of immunity. In this regard, opsonins played an especially important role as both an experimental and conceptual bridge between the competing schools. What was no longer under consideration (and in fact never was explicitly debated) concerned the intellectual foundation of Metchnikoff's original concept of immunity as those activities that defined organismal identity, (developed from Metchnikoff's research in developmental biology) and which regarded host defense mechanisms as only subordinate to this primary function. Immunology in the first half of the 20th century pursued issues pertinent to chemically characterizing immune specificity and only later returned to the Metchnikovian question of how the immune identity was established. This latter venture has achieved molecular sophistication, but even such a formulation may be an inadequate answer to the Metchnikovian postulate. The theoretical discussion between cellularists and humoralists continues in new guises, for the essential debate remains unresolved.     

The birth of immunology: Metchnikoff, the embryologist

Metchnikoff must be viewed first as an embryologist, who, influenced by the Darwinian currents of the 1860s and 1870s, sought to establish a genetic and embryologic unity in phylogeny. His principal early theory that the mesoderm was the origin of endodermal structures enabled him to extend the observation of mesodermal digestive processes to a theory of immunity. Observation of amoeboid phagocytosis was not novel, but Metchnikoff's scientific investigations had prepared him to interpret this activity as a manifestation of a generalized property of the mesoderm. Earlier observers noted the presence of microorganisms and particles in leukocytes, and the notion of phagocytosis had previously been entertained, but only Metchnikoff recognized the importance of phagocytosis in a general scheme of inflammation and to develop an experimental model for its investigation. The observation was thus viewed not solely as an issue of pathology, but rather as a contribution to Metchnikoff's general idea of genetic unity and his hypothesis of a primordial multicellular organism, Parenchymella, later called Phagocytella. It is striking that he ultimately viewed phagocytosis as a question of immunity, considering the context of his research activities, which had been confined to evolution and biology of development. To demonstrate how the famous Messina experiments were extended to a new theory of immunity requires formulating Metchnikoff's recognition of both the importance of phagocytosis for his mesodermal theory and a more general theory of pathology. The result was the genesis of a new idea, immunity.     

Pasteur, Pastorians, and the dawn of immunology: the importance of specificity

Throughout his career, the problems that attracted Louis Pasteur almost invariably involved considerations of specificity of structure and/or of action. Thus, his work on asymmetric crystals showed that chemical form not only specifies crystalline structure, but affects the affinity of ferments as well. In his studies of diseases of silkworms, of beer, and of wine, he could unerringly distinguish with the microscope the specific agents of disease. From this emerged his concept of the specificity of species and against the nonspecificity of spontaneous generation, whence the germ theory of disease. It was in the new field of immunology, however, where the manifestations of an exquisite specificity were most clearly seen. Here, Pasteur's vaccines worked because he chose the specific pathogen in order to induce a specific immunity, and he succeeded each time. But the two most prominent Pastorian successors in immunology, Elie Metchnikoff and Jules Bordet, were not equally successful. Although each contributed significantly to the birth of immunology, each advanced a theory that neglected the principle of specificity and paid a price in consequence. Metchnikoff's phagocytic theory of immunity could not survive the demonstrable specificity of humoral antibodies, while Bordet's physical adsorptive concept of the antibody-cell interaction quickly fell to Paul Ehrlich's demonstration of the stereochemical determination of immunological specificity.     

I. I. Mechnikoff's contribution to immunology

I. I. Mechnikoff's contribution to various aspects of immunology is evaluated. The 25 years' struggle of this scientist for the existence of phagocytosis theory is briefly described. Works of I. I. Mechnikoff dealing with several factors of humoral immunity and cytotoxins are reviewed. The significance of I. I. Mechnikoff's studies providing analysis of immune processes in the phylogenetic sense as well as his ideas about the nervous system role in immunity processes is stressed.     

Role of the mannose receptor in the immune response

The mannose receptor (MR) recognizes a range of carbohydrates present on the surface and cell walls of micro-organisms. The MR is primarily expressed on macrophages and dendritic cells and is involved in MR-mediated endocytosis and phagocytosis. In addition, the MR plays a key role in host defense and provides a link between innate and adaptive immunity. Herein, we will review the role of the MR in innate host defense as well as the recent evidence for its role in the adaptive response, for both humoral and cellular immune responses.     

Induced humoral immunity and vaccination against major human fungal pathogens

Protection against fungal pathogens can theoretically be elicited by vaccines that stimulate humoral or cellular immunity, or both. There is conclusive evidence that humoral immunity can modify the course of infection against certain pathogenic fungi such as Candida albicans and Cryptococcus neoformans. However, for other fungi, such as Aspergillus fumigatus, the notion that humoral immunity contributes to host defence is unproven. Attempts to evaluate the potential efficacy of humoral immunity using immune sera are often inconclusive, whereas consistent results can be obtained with monoclonal antibodies. Protective monoclonal antibodies can be used to identify antigens that induce useful humoral responses.     

Interaction of two phagocytic host defense systems: Fcγ receptors and complement receptor 3

Phagocytosis of foreign pathogens by cells of the immune system is a vitally important function of innate immunity. The phagocytic response is initiated when ligands on the surface of invading microorganisms come in contact with receptors on the surface of phagocytic cells such as neutrophils, monocytes/macrophages, and dendritic cells. The complement receptor CR3 (CD11b/CD18, Mac-1) mediates the phagocytosis of complement protein (C3bi)-coated particles. Fcγ receptors (FcγRs) bind IgG-opsonized particles and provide a mechanism for immune clearance and phagocytosis of IgG-coated particles. We have observed that stimulation of FcγRs modulates CR3-mediated phagocytosis and that FcγRIIA and FcγRI exert opposite (stimulatory and inhibitory) effects. We have also determined that an intact FcγR immunoreceptor tyrosine-based activation motif is required for these effects, and we have investigated the involvement of downstream effectors. The ability to up-regulate or down-regulate CR3 signaling has important implications for therapeutics in disorders involving the host defense system.     

The genius of E. E. metchnikoff— Discoveries over the centuries

On the 15 of May we celebrated the 150th anniversary of the outstanding Russian biologist Elias E. Metchnikoff (1845–1916)—Nobel Prize winner (1908), full and honorary member of many scientific academies of the world. His main works were applied to the zoology of invertebtates, evolution, embryology, immunology, microbiology, infectious pathology, gerontology, etc. Elias Metchnikoff published essays on anthropology, theory of orthobiosis, role of social and social-hygienic factors in solving the problems of old age and life elongation. On 30 May-2 June 1995 an International Symposium dedicated to Metchnikoff's 150th anniversary was held in Moscow. This is a text of the lecture given by us at the opening ceremony.     

Study of the immunotropic activity of aminoglycoside antibiotics

The action of some aminoglycoside antibiotics on the immune system was studied on both intact mice and the animals with immune deficiency caused by administration of cyclophosphamide. The following tests were used: local hemolysis (the Herne test), lymphocyte transformation (LT), delayed hypersensitivity to sheep red blood cells and the local graft versus host reaction (GVHR). Amikacin was shown to have no significant action on the activity of lymphocytes in the intact mice and stimulated both cellular (LT and GVHR) and humoral (the Herne test) immunity in the animals with lowered immunological reactivity. Sisomicin had no significant action on the immune system of the animals. Gentamicin suppressed the immune response only in the intact mice. Kanamycin and streptomycin induced inhibition of humoral and cellular immunity in both the intact mice and animals with immune deficiency. On the basis of the results it was concluded that gentamicin, amikacin and sisomicin may be used in the treatment of diseases developing in the presence of immune deficiency whereas streptomycin and kanamycin should be recommended when inhibition of the immunity is needed.     

Cadmium exposure of rainbow trout, Salmo gairdneri Richardson: effects on immune functions

Differential leucocyte counts, phagocytosis, humoral antibody response and the in vitro blasto-genetic response to mitogens (lipopolysaccharide and Concanavalin A) and to an antigen ( Vibrio anguillarum ) were studied in rainbow trout exposed to 0,0.7 or 3.6 μg Cd 1⁻¹ for 12 weeks.
Although the fish did not exhibit any clinical or histological changes, cadmium exposure was found to affect two of the immune parameters measured. The cellular response of fish immunized with V. anguillarum to the homologous antigen was significantly lower for splenocytes obtained from fish exposed to cadmium for 9 weeks (3.6 μg Cd 1⁻¹ group) than for splenocytes obtained from non-exposed fish. Conversely, the humoral antibody response to V. anguillarum O-antigen was higher in the 3.6 μg Cd 1⁻¹ group than in the non-exposed group. Protective immunity of fish vaccinated against V. anguillarum was equally as good in the cadmium-exposed group as in the non-exposed group. No cadmium-induced changes in differential leucocyte counts or in the proportions of phagocytic cells were observed.     

Targeting melanoma inhibitor of apoptosis protein with cancer immunotherapy

Aberrantly expressed or mutated proteins in cancer cells evoke immune recognition, but host reactions are usually insufficient to prevent disease progression. Vaccination with irradiated tumor cells engineered to secrete granulocyte-macrophage colony stimulating factor (GM-CSF) augments host immunity through improved tumor antigen presentation by recruited dendritic cells and macrophages. By analyzing the immune response of a metastatic melanoma patient who achieved a long-term response to vaccination, we identified melanoma inhibitor of apoptosis protein (ML-IAP) as a target for immune-mediated tumor destruction. Vaccination stimulated a coordinated cellular and humoral reaction to ML-IAP that was associated with extensive tumor necrosis, whereas lethal disease progression was linked with the loss of ML-IAP expression and the absence of intra-tumoral lymphocyte infiltrates. These findings demonstrate that ML-IAP can serve as a tumor rejection antigen, although additional vaccine targets will be required to circumvent immune escape and tumor heterogeneity.     

Lead induced modulation of splenic macrophage responses on humoral and cell mediated immunity

The heavy metal lead is an environmental toxic material that can induce pathophysiological changes in many organ systems. Previous studies have shown the effects of lead exposure on immune cells in different experimental animals, however, the mechanism of their influence on the immune system is unclear. We reported that in vivo lead exposure inhibits phagocytosis, nitric oxide release, induces DNA fragmentation suggesting the apoptotic death of the target cell. We have also presented evidence that inhibition of macrophage functional responses implicated alteration of humoral and cell mediated immunity. In vivo exposure to lead acetate alters the phagocytic capacity of splenic macrophages as evident from the reduction of phagocytic index of control from 19,792+/-1385.69 to 8893+/-893 in the treated group. The amount of nitric oxide released by the control cell 2.25+/-0.125 microM is also reduced to 1.9375+/-0.0625 microM upon in vivo lead treatment. Functional integrity of the target cell is also decreased after lead exposure as obtained from the percentage of DNA fragmentation. Control group shows 33.29+/-0.11% of fragmented DNA, which is enhanced to 42.43+/-0.725% following the lead treatment. A greater percentage of DNA fragmentation upon lead treatment probably indicating that the heavy metal induces apoptosis. The humoral immune response is also altered after lead exposure as indicated by the decrease of the antibody titre in control group from 1:2048 to 1:128 in the treated group. From the DTH reaction, it was observed that the mean diameter of swollen foot pad of control mice is 0.329+/-0.15 cm and that of lead treated mice is 0.274+/-0.056 cm. It can, therefore, be suggested that lead inhibits normal functional activities of splenic leukocytes, particularly phagocytosis and also affects the functional integrity of cells by inducing DNA fragmentation. The study may demonstrate the usefulness of investigation of humoral immune system and leukocyte functions as sensitive parameters in detecting the effects of lead toxicity.     

双歧杆菌对小鼠单核吞噬细胞功能的影响

双歧杆菌是革兰氏阳性无芽胞厌氧菌,是人和动物肠道的正常菌群之一。我们研究了注射双歧杆菌对小鼠单核吞噬细胞功能的影响。注射婴儿双歧杆菌和青春双歧杆菌后小鼠腹腔巨噬细胞酸性磷酸酶含量增加、吞噬试验的吞噬率及吞噬指数明显提高,表明双歧杆菌能增加巨噬细胞吞噬消化功能,以婴儿双歧杆菌为启动剂可从DBA/2小鼠体内诱生肿瘤坏死因子,提示双歧杆菌可调节单核吞噬细胞分泌细胞因子。因此双歧杆菌能激活单核吞噬细胞,促进机体的免疫学反应。推测定居于肠道的双歧杆菌可能是通过移位到体内器官、释放免疫活性成分被肠道中Peryer氏淋巴结群内的巨噬细胞吞噬,从而作用于机体单核吞噬细胞系统。这一推测尚需进一步研究证实。     

Bacterial infection modulated by glucan: A search for the host defense potentiation mechanisms

Interactions between bacteria and the host were studied from day 0 up to day 10 post-challenge in mice pretreated with soluble glucan (20 mg/kg i.p.) and challenged supralaryngeally with a virulent strain ofKlebsiella pneumoniae. In the initial phase of infection, clearance of bacteria in the airways of glucan-treated mice was improved to an extent comparable with the vaccinated group but, in contrast to the immunized animals, subsequent regrowth of the bacterial inoculum was not prevented. The efficacy of defense, based during the entire course of infection mainly upon phagocytosis by neutrophils, markedly increased at intervals corresponding to the onset of humoral immune response. No evidence was obtained to indicate an enhanced involvement of alveolar macrophages in the phagocytosis of bacteria in glucan-stimulated mice. The results further support the notion that improvement of specific immune responsiveness rather than activation of nonspecific effector functions might be the most important expression of the host-defense-potentiating capacity of glucan and related stimulants of microbial origin.     

Immune depression--a possible cause of the unfavorable course of pneumonia in chronic alcoholics

In 27 patients, suffering with chronic alcoholism and hospitalized for pulmonary diseases in the Clinic of Pulmonology and Phthisiology, the following immunological characteristics were checked up: the functional activity of polymorphonuclear leukocytes and in 12 patients also that of alveolar macrophages were evaluated on the basis of the study of the phagocytic index and the phagocytic number, myeloperoxidase and the nitro blue tetrazolium test; the levels of serum IgG, IgA and IgM, the titer of the complement, E-rosette-forming cells (active and total) were also evaluated; the deficiency of cell-mediated immune response was determined by means of intradermal tests with the use of P.P.D., phytohemagglutinin, candidin, trichophytin. In all these investigations the depression of the functional activity of polymorphonuclear leukocytes and alveolar macrophages, dysimmunoglobulinemia, the increased level of circulating immune complexes and the suppression of cell-mediated immunity characteristics were revealed in the patients. Frequent infections and the severe course of bacterial and viral infections observed in such patients can be probably attributed to deficient cell-mediated immune response and to disturbances in phagocytosis.     

Immunomodulatory activity of methanolic extract of Murraya koenigii (L) Spreng. leaves

Immunomodulatory activity of methanolic extract of M. koenigii leaves was evaluated on humoral and cell mediated immune response to ovalbumin, phagocytic activity by carbon clearance test, nitric oxide (NO) release from murine peritoneal macrophages and cyclophosphamide induced myelosuppression. Significant increase in the NO production by mouse peritoneal macrophages was detected in culture supernatants indicated increased phagocytic activity of macrophages. The extract showed significant increase in phagocytic index by rapid removal of carbon particles from blood stream. The extract also increased the antibody titre against the ovalbumin and protection towards the cyclophosphamide induced myelosuppression. However, the extract did not show any significant increase in delayed type hypersensitivity reaction which indicated the inability of the extract to stimulate T cells. Present study thus reveals that the extract holds promise as immunomodulatory agent, which acts by stimulating humoral immunity and phagocytic function.     

Suppression of Splenic Lymphocyte Proliferation by Eucommia ulmoides and Genipin

We investigated the modulation of innate and adaptive immune cell activation by Eucommia ulmoides Oliver extract (EUE) and its ingredient genipin. As an innate immunity indicator, the phagocytic activity of macrophages was determined by measuring engulfed, fluorescently labeled Escherichia coli. As a surrogate marker for the respective activation of cellular and humoral adaptive immunity, concanavalin A (Con A) and lipopolysaccharide (LPS) induction of primary splenocyte proliferation was assayed in in vitro and ex vivo systems. EUE and genipin suppressed the proliferation of primary splenic lymphocytes induced by Con A or LPS, but not macrophage phagocytosis. Oral administration of EUE and genipin to mice decreased splenic lymphocyte proliferation induced by Con A or LPS. These results revealed that E. ulmoides and genipin suppressed cellular and humoral adaptive immunity, and they suggest that E. ulmoides and genipin are promising candidates for immunosuppressive drugs that target diseases that involve excessive activation of adaptive immunity.     

Bacterial determinants of persistent throat colonization and the associated immune response in a primate model of human group A streptococcal pharyngeal infection

Group A streptococcal (GAS) pharyngitis and the subsequent bacterial colonization of the human throat elicit an immune response that may precipitate acute rheumatic fever in a susceptible host. To study the bacterial determinants that influence throat colonization and induction of humoral immunity, we characterized the behavior of GAS strains in a baboon model. An M-type 3 clinical isolate of GAS typical of strains that cause pharyngitis and invasive infection was recovered from the pharynx of six out of six baboons for at least 6 weeks after oral inoculation. By contrast, an isogenic mutant deficient in M protein failed to colonize most animals or was rapidly cleared. An isogenic mutant deficient in hyaluronic acid capsule colonized five out of six animals, but only persisted in the pharynx for 14–21 days. Colonized animals developed serum anti- streptolysin O (SLO) and anti-M protein immunoglobulin (Ig)G. The kinetics of the antibody responses were similar to those seen after human infection. Peak titres increased with the duration of throat carriage. Colonization with GAS prevented recurrent colonization after challenge with the homologous wild-type strain, but not after challenge with a strain of different M protein type. Early clearance of the M protein-deficient strain was associated with increased susceptibility of this strain to phagocytic killing in non-immune serum, whereas clearance of the acapsular strain was associated with increased susceptibility to phagocytic killing in the presence of specific antibody. These studies support critical and distinct effects of the GAS M protein and capsule on throat colonization and induction of humoral immunity in a model that reproduces important features of pharyngeal colonization and immune response following human infection.     

果蝇先天性免疫研究进展

果蝇是生命科学与人类疾病研究的重要模式生物,虽然不具有人类高度专一的获得性免疫,但也有对病原微生物感染作出快速有效反应的先天性免疫应答系统,主要包括体液免疫,细胞免疫和黑化反应。文章结合国外最新研究,详细介绍果蝇体液免疫中控制抗菌肽合成的Toll信号通路和Imd信号通路中涉及的蛋白及其相互作用,并对果蝇细胞免疫中的吞噬、包埋功能和黑化反应作简要阐述。研究表明,果蝇的Toll和Imd信号通路分别与人类的TLR4和TNRF-1信号通路存在着惊人的相似之处,说明果蝇与人类在免疫调控通路方面可能存在着共同的进化起源。