Kwok-Choy Lee

On the origin and mode of action of functionally distinct macrophage subpopulations

SummaryFunctionally distinct subpopulations of macrophages at various stages of differentiation can be separated by fractionation of murine peritoneal cells according to size, since the maturation of monocytes into macrophages is associated with cell enlargement. For immunostimulatory functions which can be served by macrophage-derived factors, normal macrophages of all sizes will function very well. However, in the antigen-specific T cell proliferative response which requires the presentation of antigen on the surface of macrophages bearing determinants (Ia) specified by the I-region of the major histocompatibility complex, only small, and hence relatively immature, macrophages will stimulate. This antigen-presenting activity is predictably sensitive to treatment with antisera specific for Ia. Intraperitoneal administration of the adjuvant, Corynebacterium parvum, induces the appearance of cytostatic and cytolytic activity against tumor cells. This activity is associated with the largest macrophages which are separable from the small, immunostimulatory macrophages. Thus the maturation of monocytes can be envisaged as following a linear sequence from the Ia+ antigen-presenting cells to the cytocidal activated macrophages. An alternative approach to the problem of macrophage heterogeneity is the cultivation of macrophages from bone marrow precursors in vitro. Antigen-presenting activity develops during the exponential phase of growth to varying degrees depending on the source of the colony stimulating factor used in the bone marrow cultures and on the antigen used for immune stimulation. Although culture-grown macrophages are as active as normal splenic or peritoneal macrophages at presenting large antigens, they are clearly deficient at presenting small antigens. Cell size fractionation of exponentially growing bone marrow cultures has revealed that the antigen-presenting cells are small macrophages, but their position in the cell cycle and their developmental relationship to macrophages in vivo have not been elucidated.

The cellular basis of cortisone-induced immunosuppression of the antibody response studied by its reversal in vitro.

Spleen cells from mice pretreated with cortisone were impaired in their ability to support an immune response in vitro to two antigens: sheep erythrocytes (SRBC) and polymeric flagellar protein of Salmonella adelaide (POL). We conclude that this immunosuppression is consistent with cortisone causing a dysfunction in accessory cells (macrophages?) and thymus-derived (T) helper cells without seriously affecting antibody forming cell precursors. Evidence for this comes from reconstitution of the response with additions of peritoneal exudate cells (PEC, irradiated, and anti- θ -treated), activated T cells, and 2-mercaptoethanol (2-Me) in culture. Additions of PEC or 2-Me restored the T cell-independent anti-POL response not only in cortisone-treated spleen cell cultures, but, contrary to previous reports, also in cultures of normal spleen cells depleted of adherent (accessory) cells by carbonyl iron treatment. The anti-SRBC response (which is dependent on T cells and accessory cells) in cortisone-treated spleen cell cultures was fully restored only by a combination of activated T cells and PEC or activated T cells and 2-Me. However, with lower doses of cortisone pretreatment, activated T cells or 2-Me alone was effective.

Antigen-specific murine T-cell proliferation: Role of macrophage surface Ia and factors

Abstract The proliferation of Mycobacterium -primed murine lymph node T cells to purified protein derivative of tuberculin (PPD), as measured by the uptake of tritiated thymidine, requires the obligatory participiation of macrophages which stimulate the T cells either directly with antigen in association with cell surface Ia (I region-defined antigens), or indirectly by means of soluble factors. We have examined the possibility that this functional dichotomy is due to heterogeneity within the macrophage population. Since the maturation of macrophages from the precursor monocytes is associated with cell enlargement, macrophage subpopulations differing in developmental stage are obtained by cell fractionation according to size by velocity sedimentation. Nylon-wool-purified T cells which have been depleted of macrophages and B cells are stimulated with PPD either in a free form or bound to macrophages which have been incubated for a short time (i.e., pulsed) with PPD. We found that for PPD-pulsed macrophages, only the smallest (and probably the most immature) are capable of inducing T-cell proliferation. This antigen presentation function is mediated by cell surface Ia since it is abolished by pretreatment of the macrophages with anti-Ia serum and complement. On the other hand, all macrophages, irrespective of sensitivity to anti-Ia serum, secrete factors which will stimulate T-cell proliferation in the presence of free PPD. Thus the maturation of macrophages is accompanied by a shift from Ia-dependent to Ia-independent mechanisms of immunostimulation.

Separation of functionally distinct subpopulations of Corynebacterium parvum-activated macrophages with predominantly stimulatory or suppressive effect on the cell-mediated cytotoxic T cell response

Abstract Peritoneal cells (PEC) from mice injected ip with Corynebacterium parvum (CP) showed greatly enhanced suppressive activity on the growth of syngeneic tumor cells and on the generation of alloreactive cytotoxic T lymphocytes (CTL) in vitro . On the other hand, CP-activated PEC exhibited increased immunostimulatory (accessory or A cell) activity as measured by the restoration of the CTL response of nonadherent spleen cells. After fractionation of the CP-activated PEC according to cell size by velocity sedimentation, the mutually antagonistic A cell and immunosuppressive activities were clearly separated and found to be associated with functionally distinct subpopulations of macrophages. Thus A cell function was detected in fractions rich in small and medium sized macrophages which were probably derived from recently arrived monocytes. Immunosuppressive (and anti-tumor) activity was associated with the largest macrophages which were almost devoid of A cell function and probably represented a highly activated and differentiated macrophage subpopulation.

Accuracy of physical examination using the rib-pelvis distance for detection of lumbar vertebral fractures

Clinical vertebral fractures, which are usually detected when patients present with back pain, account for less than one third of all vertebral fractures (1–5); the rest are occult and go undetected during routine nonradiologic evaluations. However, both clinical and occult vertebral fractures are associated with important health consequences (4 –12), and one of the challenges in improving care for patients with osteoporosis is enhancing the detection of occult vertebral fractures, such as during the physical examination (12–16). A decrease in height or a marked accentuation of the dorsal kyphosis suggests the presence of vertebral fractures (13,16). Little is known about how to detect fractures in the lumbar spine on clinical examination, although the first four lumbar vertebras account for 40% of all vertebral fractures. Because the decreased height of a fractured lumbar vertebra reduces the distance between the inferior margin of the ribs and the anterior superior iliac crest of the pelvis (16 –21), we evaluated the accuracy of using the rib-pelvis distance for detecting lumbar vertebral fractures.

High Incidence of IDDM Over 6 Years in Edmonton, Alberta, Canada

OBJECTIVE To determine the incidence of IDDM among children 0–14 years of age in Edmonton, Alberta, between 1990 and 1995 by means of a population-based registry. RESEARCH DESIGN AND METHODS Children <15 years of age diagnosed with IDDM between January 1990 and December 1995 were registered according to criteria of the World Health Organization (WHO) Multinational Project for Childhood Diabetes. The primary source of case ascertainment consisted of office records of pediatricians and endocrinologists. The secondary source consisted of inpatient records from the main city hospitals. RESULTS Between 1990 and 1995, 211 IDDM patients <15 years of age were detected by the two sources. All but 15 of them were of European ancestry. The ascertainment-corrected incidence rates of this ethnic group (constituting 77% of the population) for the 6 years were 38.6, 23.5, 23.3, 24.2, 22.0, and 24.3 per 100,000, respectively, with case ascertainment rates of 75–95%. The age-adjusted rate over the 6-year period was 25.7 per 100,000 with a case ascertainment rate of 84.3%. No sex difference was observed. The highest incidence occurred in the 10- to 14-year-old age-group, and more cases were detected between January and March than at other periods in the year. CONCLUSIONS The incidence of IDDM among the European-derived population in Edmonton between 1990 and 1995 is the highest rate over a 6-year period to be reported in North America, comparable to that in Prince Edward Island, Canada, and to the highest rates in the world.

Regulation of constitutive and lymphokine-induced Ia expression by murine α-fetoprotein

Abstract α-Fetoprotein (AFP) has been shown to suppress a variety of immune responses in vitro . The immunosuppressive properties of AFP can be partly attributed to the ability of this protein to decrease the cell surface expression of Ia antigens on macrophages. The experiments described in this report define more precisely the regulatory effects of AFP on Ia expression. Using the “dendritic-like” cell line P388 AD2 and bone marrow-derived macrophages we have shown that AFP can suppress the constitutive expression of cell surface Ia antigens. This decrease is detectable on the cell surface 24 hr after the addition of AFP. In further experiments we also examined the effect of AFP on lymphokine-induced Ia expression. Our results show that AFP has no suppressive influence on the inductive phase of lymphokine-induced Ia antigen expression but can decrease elevated levels of Ia antigen subsequent to their induction.

The role of macrophages in B cell tolerance: I. Antigen-specific failure of Thy-1, Ly-2 negative adherent cells from tolerant mice to reconstitute immunocompetence in adherent cell deficient spleen cells☆

T-Cell-independent B-cell tolerance to the hapten derivatives of carboxymethyl cellulose (CMC) or methyl cellulose (MC) appears to be controlled by Thy-1-, Ly-2- adherent (A) cells contained in the spleen or peritoneal fluid. Immunocompetence in nonadherent (NA) normal spleen cells could be restored in vitro by irradiated A cells from normal mice. However, NA cells reconstituted with irradiated A cells derived from hapten specifically tolerant mice failed to respond to the same hapten, but responded normally to an immunogenic challenge with another unrelated antigen. A cells that had been preincubated at 4 degrees C with hapten derivatized MC also failed to restore immunocompetence. While preincubation of unfractionated spleen cells with the tolerogen under the same conditions resulted in B-cell unresponsiveness, such treatment of NA cells failed to render B cells tolerant. Treatment of A cells from tolerant mice with the reducing agent potassium iodide (KI) in vitro restored their capacity to render cultures of NA cells immunocompetent to the relevant hapten. Moreover, treatment with KI of spleen cells from mice injected with the tolerogen was shown to render them responsive. We suggest that B-cell tolerance induced by hapten derivatives of CMC and MC is mediated by suppressive macrophages contained among A cells. Certain subpopulations of macrophages are known to exert cytotoxic effects upon target cells by the release at close range of oxidating agents. We postulate that hapten derivatized CMC and MC, through unique properties of the carrier, bind to and possibly activate macrophages rendering them specifically suppressive for hapten binding B cells.