INTRODUCTION:
Echinacea is a herb originally used by Native Americans to cure wounds, snakebites and as a blood purifier. Today it is commonly used as a home remedy to treat upper respiratory tract infections and during cancer treatment. Echinacea is most effective when taken during the first symptoms of the common cold. Indeed research in our laboratory has shown that Echinacea can stimulate macrophages, which are white blood cells involved in destroying foreign pathogens. Mice that were infected with Listeria usually succumbed to this infection. However, when these mice were treated with Echinacea they were able to clear the Listeria infection and subsequently survived. Listeria is an intracellular pathogen, which we know is primarily cleared by activated macrophages. From this it was concluded that Echinacea must activate macrophages, which are involved in protecting the host from bacterial infection.

The hypothesis that Echinacea was responsible for macrophage activation and conferring protective immunity on infected mice was tested by measuring the production of pro-inflammatory cytokines including Interleukin-6 (IL-6) and Tumor Necrosis Factor-alpha (TNF-a), which are known to be produced by activated macrophages. Indeed, macrophages treated with Echinacea produced large amounts of IL-6 and TNF-a as compared to untreated controls. Under the light microscope, it was then observed that these macrophages underwent changes in their morphology upon treatment with Echinacea. The macrophage (J774) tumor, on which these experiments were performed, changed from a smaller, round cell resembling a monocyte to a larger, more mature, spindle-shaped macrophage. It was also observed that the cells were not as densely populated after treatment with Echinacea. These findings stimulated the examination of the proliferative response of this macrophage tumor after treatment with Echinacea. This experiment confirmed that the proliferation of this macrophage tumor had indeed been inhibited after stimulation with Echinacea. This was of particular interest because it demonstrates that Echinacea is able to inhibit the growth of a tumor and could be evaluated as a potential cancer treatment.

All cells originate from a common pluripotent stem cell, which differentiates into another stem cell or a more specialized cell through the activation of certain genes. The macrophage is produced in the bone marrow from a myeloid stem cell. It circulates in the blood as a monocyte before entering the tissues at a site of inflammation and differentiating into a macrophage. During an immune response to offending pathogens, macrophages become activated by stimuli such as cytokines including Interferon Gamma (IFN-?), which are produced by T-cells, and bacterial components such as lipopolysaccharide (LPS). When activated, macrophages also produce cytokines that in turn activate T cells and other cells of the immune system. These cytokines include Interleukin-1 (IL-1), Interleukin-6 (IL-6), Interleukin-10 (IL-10) and Tumor Necrosis Factor-alpha (TNFa). Other than cytokine production, macrophages also actively engulf pathogens by pulling them inside and destroying them in a process called phagocytosis. As well, they secrete inflammatory mediators and cytotoxic proteins, which eliminate virus-infected cells, tumor cells and intracellular bacteria.

A neoplasm or tumor is formed when the genes involved in controlling the cell cycle and division of a cell, are altered or blocked. The cell enters the cell cycle and is caught in a stage of development leading to uncontrollable proliferation. As a cell matures and becomes more committed to its lineage its proliferative capacity decreases. Therefore, if a cell is unable to terminally differentiate, it remains active within the cell cycle and continues to divide. The exact cause of tumor genesis is not completely understood, however both the external environment and hereditary factors are known to play a role in tumor development. Malignant tumors not only proliferate uncontrollably, but they invade other tissues, and are commonly referred to as cancer. Leukemia is the uncontrollable proliferation of blood cells and inevitably leads to failure of bone marrow to produce other needed blood cells. It is subdivided into either myelogenous or lymphogenous leukemia and is based on the type of cell which has become neoplastic. Acute myelogenous leukemia (AML) occurs in approximately 13 of 100,000 people every year. It is commonly fatal if left untreated or if diagnosed at an advanced stage. Potential causes of AML include radiation exposure, and aromatic hydrocarbons such as benzene or chemotherapeutic drugs. In this type of cancer, promyeloid cells are blocked at an early stage of development and are thus capable of vigorous proliferation. They start to proliferate in the bone marrow where they originate, accumulate and then migrate to the blood stream and into tissues such as lymph nodes, the spleen, the skin or the central nervous system. Healthy myeloid cells differentiate into erythrocytes (red blood cells), and certain leukocytes (white blood cells). Thus, AML disturbs hematopoiesis, the production of erythrocytes, and the leukocyte controlled immunity of the organism. It has been found that Type Three (M3) AML can be treated with retinoic acid. Treatment of M3 AML with retinoic acid causes cells to mature and regain their normal growth characteristics, whereby they undergo programmed cell death (PCD) or apoptosis after a certain time limiting their proliferative capacity. It is not yet known exactly how retinoic acid causes maturation in these tumors. However, no treatment is completely effective in limiting the growth of tumors and as such the search continues for other agents, which may be used to effectively treat this terrible disease.

In order to maintain homeostasis in the body, programmed cell death (PCD), which is also known as apoptosis, must take place. This is a natural, gene controlled process, which eliminates aging and damaged cells. In this process the cell begins to shrink, the DNA fragments, the endoplasmic reticulum (ER) dilates, and the cell slowly breaks off into small membrane bound vesicles known as apoptotic bodies. Cells such as macrophages or dendritic cells then phagocytose the apoptotic bodies. Apoptosis is needed for proper development of the body. For example, to form a synapse, or gap between two neuron ends, cells must be eliminated through apoptosis. Another example is the formation of fingers and toes. In the fetus the hand is a mass of cells from which some must be removed by apoptosis to form individual fingers.

Cell death is either mediated by the immune system or by the cell itself. If a cell is infected with a virus, the cells of the immune system are responsible for killing it to protect the organism. One method whereby potentially dangerous offending pathogens are eliminated is the induction of apoptosis. Cytotoxic molecules produced by immune cells including macrophages target virus infected cells leading to apoptosis. Death activator molecules include Tumor Necrosis Factor Alpha (TNF-a). These molecules are secreted by macrophages and bind their respective receptors on the target cell resulting in the transduction of an intracellular signal. Subsequently, there is initiation of the caspase system, which leads to activation of several enzymes, which trigger DNA destruction and apoptosis. This series of activated proteases digests the essential proteins in the cell and leads to cell death. This immune mechanism is also used to destroy tumor cells or damaged host cells.

The cell itself can induce apoptosis, by one of the many cell growth and death regulating genes, which can initiate apoptosis by activating the caspase system. A common gene known to control apoptosis is p53. Tumor cells are unable to undergo apoptosis because p53 and other genes are mutated or blocked in order for the tumor cell to continue proliferation.

It was hypothesized that Echinacea, like retinoic acid, could induce maturation and lead to apoptosis in leukemic cells. One way of looking at maturation of cells is to examine their surface marker expression such as the Major Histocompatibility Complex (MHC) molecule. It is also known as the Human Leukocyte Associated Antigen (HLA) in humans. These molecules are specific to an individual and are divided into two major classes allowing the host to distinguish between self and non-self. The class I MHC molecule is displayed on all cells of the body, whereas Class II MHC is expressed by antigen presenting cells, which are necessary for the initiation of an immune response. The MHC molecule is a protein with an antigen found in its groove. This antigen reveals information about the cell to which it is attached. Only T-cells, which have the surface marker CD8, can recognize MHC class I molecules and read the displayed antigen. The second class of the MHC molecule becomes up regulated in macrophages as they become activated in order to serve their function of initiating immune responses. MHC class II molecules also contain antigens in their grooves. The peptides presented by the MHC class II molecules are not produced inside the presenting cell as in the case of MHC class I molecules. These peptides are taken up from the extra cellular environment through endocytosis, processed inside the cell and presented on the surface of the presenting cell. CD4+ T-cells read MHC class II molecules and become activated. Their activation can initiate both a humoral response, in which B-cells produce antibodies and a cell mediated response in which cells such as cytotoxic T-cells, macrophages and neutrophils destroy the offending pathogen.