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Lab 2. Methods of Leukocyte fractionation: Enrichment: 1. Fluorescence activated cell sorting (FACS) -cost, -availability of equipment -markers may be on more than one cell type e.g. MHC class II on APCs (DC, M, B cells) -markers may not be on a cell type
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1. Fluorescence activated cell sorting (FACS)
-availability of equipment
-markers may be on more than one cell type
e.g. MHC class II on APCs (DC, M, B cells)
-markers may not be on a cell type
e.g. no Ig on plasma cells
-availability of Abs or MHC tetramers
(don’t have antibodies for cell surface markers in many species)
Antibody identifies specific cell type (eg. CD3+ T cells)
Tetramer of MHC class I with specific peptide for isolation of specific T cells (eg. influenza specific CD8+ T cells)
2.a Magnetic sorting
The magnetically labeled fraction is recovered by applying the vessel to an external magnet.
The magnetic fraction can be washed and isolated for subsequent use in downstream procedures,
or the supernatant is recovered for further use.
The splenocytes are washed (following removal of erythrocytes by osmotic shock) and incubated with
anti-CD43 and anti-Mac-1 antibody-conjugated microbeads (Miltenyi Biotec).
The bead-bound cells (positive fraction) are separated from unbound cells (negative fraction).
-C’ mediated lysis of a non-target cell- need Abs
4. Enrichment in vivo -e.g. peritoneal priming and lavage
5. Removal of cells adherent to nylon wool.
(monocytes stick to nylon wool)
-cell fractionation by differential fractionation
-density gradient fractionation
7. Discontinuous gradient centrifugation-
-granulocytes, RBCs and other dense cells removed
-physical characteristics may not distinguish cell types
8. Cytospin to concentrate, stain and visualize cells.
DENSITY is the mass per unit volume of a substance, often expressed in g/ml.
DIFFERENTIAL CENTRIFUGATION separates particles on the basis of their size.
By a series of centrifugations at various speeds and times, different-sized particles are sedimented
and collected from an initially homogenous suspension.
DENSITY GRADIENT CENTRIFUGATION
DENSITY GRADIENT CENTRIFUGATION is separation performed in a supporting
column of solution in which the density and solution concentration increase toward the bottom
of the centrifuge tube.
Requires a gradient maker to set up.
DISCONTINUOUS, OR STEP, GRADIENT
DISCONTINUOUS, OR STEP, GRADIENT is one composed of layers, with abrupt changes in density
and/or concentration from one layer to the next.
a. Differential centrifugation for fractionation
Fractionation of a cell homogenate to isolate nuclei or smaller parts of cell.
-Density gradient centrifugation
A gradient maker is used
to mix liquids of two densities
Close the port between the solutions. Add lower density solution to the output side,
higher density to the other. Need rapid mixing in the chamber and make sure you see
the higher concentration solution mixing in. Fill centrifuge tubes from the bottom with
liquid of increasingly higher density displacing the lower density liquid until the tube is full.
Usually a long metal syringe needle is placed in the bottom of the tube so that the density is
not really disturbed when the needle is removed.
To wash isolated cells, resuspend in media and pellet again.
Cells are pelleted intact at low speeds 400 x g for 10 minutes
Separation on a preparative scale by centrifugation
through a sucrose gradient.
Two types of
hepatitis B capsid
Separation and crystallization of T = 3 and T = 4 icosahedral complexes of the
hepatitis B virus core protein. Acta Cryst. (1999). D55, 717-720
Layering blood on Histopaque 1077
“buffy coat” or PBL
Red blood cells,
Unfractionated Blood on Histopaque
(note the undisturbed interface)
Fractionated blood on Histopaque
Red blood cells, platelets
Percoll density centrifugation for fractionation of B lymphocytes
Mature B cells
Proliferating B cells
Trout cells were layered over step gradients of 50, 60, 70% Percoll.
Western blot analysis of Pax-5 and Blimp-1 was used to test the purification. These two transcription factors display distinct and partially overlapping expression patterns during B cell differentiation.
mature (resting and early activated) B cells (Pax-5+Blimp–) reside in the 70% layer,
proliferating B cells reside in the 60% layer (Pax-5+Blimp+)
and plasma cells (Pax-5–Blimp+) reside in the 50% layer.
J Immunol. 2005 Jun 1;174(11):6608-16.
for display on a slide.
A cytospin device
Catastrophic failure of an
Always balance opposing tubes
Place test tube in centrifuge holder.
The higher the speed the more
accurately balanced the centrifuge
Never walk away from a
Balance with another test tube
filled to the same level
in the opposite holder.
Make sure you are using the correct rotor for the centrifuge.
Never exceed the maximum g force for the rotor.
Make sure you are using the correct centrifuge tube for the job.
Tubes may break if centrifuged at too high a speed.
Even plastic tubes can break if not in appropriate adaptors.
Pre-cool centrifuge and rotors.
NEVER walk away from a centrifuge until it reaches top speed.
Q. You are following a
protocol that says:
Spin cells at 400 rpm for
10 minutes. What else do
you need to know?
RCF=11.2 x r (RPM/1000)2
r in cm