|Abstract or Summary
- The echinoderm axial organ is located centrally, at the meeting point of the
animals' "circulatory" systems. This, and its unusual histology, have prompted
the implication of a number of different functions for the organ, including
circulation, excretion and host defense. None of these have been definitively
proven. Claims that starfish axial organ cells respond to antigen in an adaptive
manner, resembling the vertebrate antibody response, also remain unconfirmed.
The purpose of the work on Strongylocentrotus purpuratus presented in this
thesis was to independently test the hypothesis that the cells of the axial organ
respond to antigenic challenge. To determine if the cells are modified
quantitatively following antigen encounter, the cell types of the organ were first
classified according to morphological characteristics. Cell subpopulations were
then monitored quantitatively after in vivo exposure to several types of antigens.
Axial organ cells were also analyzed for qualitative changes; cells from antigen
exposed urchins were assayed for immunocytoadherence to antigen-coated
sheep erythrocytes. The coelomic fluids from the same animals were tested for
antigen-specific binding molecules using ELISA assays. Immunocytoadherence
and ELISA assays were validated with cells and sera from trout similarly exposed
to antigen and control treatments.
Eight subpopulations of axial organ cells were identified. Four of the cells
types resemble cells found in the coelomic fluid. A possible precursor cell to the
red spherule cell was found to be a member of the axial organ cell population.
Changes in the axial organ cell subpopulations after antigen exposure were not
significant, regardless of the type of antigen, exposure method or sample time.
Cells of the axial organs from TNP-exposed urchins did not bind TNP-SRBC's,
and the hemagglutination observed was neither TNP-inhibitable, nor dependent
on previous expoure to the TNP antigen. Coelomic fluids from several urchins
bound TNP to a greater extent than BSA, but the frequency of binding among
urchins was not dependent on their prior treatment. Titrational analysis of one
set of urchin coelomic fluids against the hapten, TNP, the carrier, LPS, or an
unrelated protein, BSA, revealed identical binding curves with each molecule.
This, in addition to a higher titer of binding molecules in the control animals
compared to antigen-injected animals, led to the conclusion that the response
The work presented in this thesis does not support the hypotheses that the
urchin axial organ cells respond to antigenic challenge either by a modification
in cell types present in the organ, or by the production of cell surface or
secreted antigen-specific binding molecules.