MacGlashan, Donald W., M.D, Ph.D.

Interests

Mechanisms of signal transduction

Past Research

For the last 20 years, this laboratory has focused on understanding the regulation of secretion from human basophils and mast cells. These two cell types are considered central participants in the allergic reaction as well as having a variety of other physiological or pathophysiological roles in other diseases. For these two cells types, there is a hallmark reaction, degranulation in response to stimulation through cell bound IgE. By electron microscopy, the transition from a resting unstimulated cell to a well degranulated version looks like the following:

Our interests lie in how the cells make the transition, i.e., the signaling mechanisms that control this dramatic cell response and the factors that regulate the extent of the reaction.

This laboratory has been involved in a wide variety of projects. Some examples, going back to the early 1980s, include:

First methods of purification of both human basophils and tissue mast cells that resulted in sufficient cells to engage in mechanistic studies of secretion.

A fruitful association with mathematical biologists involved in characterizing the nature and functional significance of the cell surface aggregating reaction leading to mediator secretion.

A long-standing project to characterize the secretion of non-granule mediators from both mast cells and basophils. For example, we first demonstrated the IgE-mediated generation of leukotrienes from both human mast cells and basophils. Studies in the mid 1990s also established some of the characteristics of cytokine secretion from these two cell types.

Studies throughout the late 1980s and 1990s have addressed whether these cells undergo secretion in an all-or-nothing manner. More generally, we have had a basic interest in the characteristics of the single cell response and how it differs from what is observed in the average population response. Much of this work centered on the characteristics of cytosolic calcium signaling.

There has also been a long history in developing a better understanding of how cytokines modify basophil or mast cell function. Much of the effort has focused on how interleukin-3 upregulates human basophil function.

Over the two decades of research, we have sought to understand the signal transduction pathways involved in secretion but, in particular (and in distinction with elegant studies others have done in cell lines), the relationship of known signaling pathways to the differences in cell function observed in the general human population.

Recent demonstration, both in vivo and in vitro, that IgE antibody regulates the expression of its own high affinity receptor on basophils.

Current Research

Currently, there are four major areas of research (along with a host of smaller developing projects). It is worth noting that the vast majority of what we do focuses on the behavior of the wild-type basophil or mast cell rather than employing a variety of cell line or animal cell models. This does not mean that we exclude studies using other types of cells but have chosen to devote precious resources to determining important characteristics of these very difficult to study cells. It should go without saying that there are a wide variety of collaborative efforts, many with members of this division.
As part of a long-standing funded NIH grant, we remain deeply involved in working out the mechanisms that down-regulate an ongoing IgE-mediated reaction in these cells. This process of down-regulation is probably related to a process that has been termed desensitization. The basic observation is that ongoing secretion is stopped before reaching maximal levels (as defined by other means). A variety of past efforts have begun to narrow down the candidate points in the signaling cascade that are affected by the desensitization process. As of yet, there are no clear cut candidate molecules that cause desensitization in human cells. Recent studies indicate that two forms of desensitization (specific and nonspecific) operate before or after, respectively, the activation of the receptor-associated kinase, syk. Current efforts seek to begin probing events preceding syk activation as well as events that lie between syk activation and the mobilization of cytosolic calcium (which is shut off in desensitized cells). A more recently funded enterprise relates to the observation that IgE antibody controls the expression of the high affinity receptor for IgE on basophils and mast cells. There are some practical implications for this piece of cell biology, in particular how it relates to the success of the new anti-IgE antibody therapy for allergies, so we are examining several aspects of the process. As usual, we are interested in the mechanism underlying the control of receptor expression by IgE.

Laboratory

Donald MacGlashan
Professor of Medicine - senior laboratory investigator
Email: dmacglas@jhmi.edu

Valerie Alexander
Senior Laboratory Technician

Natalia Vilarino
post-doctoral fellow - research on IgE-mediated desensitization

Positions Available

We are currently looking for post-doctoral fellows:

• one fellow to continue studies of IgE-mediated signaling and desensitization
• one fellow to work on the mechanisms of IgE-dependent regulation of FceRI expression
  

For the second fellow, we prefer someone with good experience in molecular biological techniques but applicants should be experienced in signaling mechanisms of some kind and be highly motivated to apply these skills to this difficult to study system. Most success comes from developing imaginative ways to improve current technologies in order to study the relatively low number of cells obtained from human blood or tissues. For example, past developments included digital microscopy and mass spectroscopy. With the collaboration of on-site mass spectroscopists, we will probably be developing new methods of protein phosphorylation detection using mass spectroscopy, so some comfort level with this type of technology may be helpful.