Download IMMUNE SYSTEM FUNCTION AND DEVELOPMENT IN BROILERS

IMMUNE SYSTEM FUNCTION AND DEVELOPMENT IN BROILERS
Gisela F. Err
Center of Excellence for Poultry Science
University of Arkansas, Fayetteville, AR 72701
Phone: 501-575-8664, Fax: 501-575-7139
[email protected]
Introduction
Significant progress has been made during the past 10-15 years in understanding the
development and function of the immune system in avian species. However, most of the
research in avian immunology has focused on egg-type chickens. This is due, in part, to
the availability of genetically defined lines, biomedical animal models, and specificpathogen-free (SPF) individuals within the egg-type chicken strains. Considering both the
differences in the genetic selection pressures imposed on meat-type versus egg-type
chickens, as well as, the observation that body weight is negatively correlated with immune
function (Han and Smyth, Jr., 1972, Parmentier et al., 1996), basic immunological norms
established in egg-type chickens may not be readily applied to meat-type chickens
(broilers).
With the continued increase in the economic importance of broilers, a better
understanding of the development and function of the immune system in these birds is
necessary. This knowledge will find direct application in breeder selection programs,
which have to include selection for early immunocompetence and high disease resistance to
meet the demands of modern intensive broiler production systems.
Although current
information on basic broiler immunology is limited, it will be the focus of this discussion.
In the first section of this paper, the basic concepts of chicken immunology will be
presented. In the second section, studies on specific (humoral and cell-mediated) immunity
in broilers will be discussed.
Abbreviations:
BCR, B cell receptor; BW, body weight; MHC, major histocompatibility
complex; SCWL, Single Comb White Leghorn; SPF, specific-pathogen-free; SRBC, sheep
red blood cell; TCR, T cell receptor (TCR1 = y6 TCR, TCR2 = otfll TCR, TCR3 = cxB2
TCR); FITC, fluorescein isothiocyanate; PE, phycoerythrin.
109
The Avian Immune System I
Vertebrates, including chickens, have basically two types of defense systems against
infectious agents. These are innate (non-specific) immunity and adaptive (specific)
immunity. Non-specific immunity is comprised of a broad spectrum of defense
mechanisms. These include: 1) physical and biochemical barriers designed to prevent
invasion by both infectious and non-infectious agents (antigens), and 2) soluble and cellular
components capable of eliminating foreign substances (antigens) which have successfully
invaded the body tissues. The cellular components of the non-specific immune system
include monocytes/macrophages, heterophils (neutrophils in mammals), basophils,
eosinophils, and natural killer cells. For the most part, non-specific immunity is very
effective in eliminating antigens. However, when non-specific immunity is not effective, it
becomes necessary to specifically focus immune reactivity on the antigen. At this point,
specific immunity is activated.
Specific immunity encompasses two aspects of immunity. These are humoral
immunity, which is carried out by antibodies, and cell-mediated immunity, which refers
primarily to T cell activity.
Lymphocytes are the cellular components of specific
immunity. There are various subpopulations of lymphocytes which are morphologically
indistinguishable but Which differ in site of development, tissue location, phenotypic
expression of cell surface molecules, and functional abilities. Chickens lymphocytes
consist of B cells, which develop in the bursa of Fabricius, and T cells, which develop in
the thymus. Both B cells and T cells express antigen receptors on their surface. Each B
cell and T cell has a homogeneous set of antigen-receptors specific for a given antigen.
Collectively, the B cell and the T cell compartment each have a repertoire of nearly 109
different antigen-specificities.
Upon the first encounter with an antigen, for example a pathogen "A", there are
relatively few T and B cells with receptors specific for the antigen. Before pathogen "A"
can be eliminated by specific immune components, T and B cells with pathogen "A"specific receptors have to proliferate and differentiate into effector cells (e.g. antibodyproducing plasma cells). However, proliferation and differentiation take time,, often giving
pathogen "A" the opportunity to cause disease. Instead of becoming effector cells, cells
lFor references concerning some basic aspects of avian immunology, see Davison et al.,
1996 (general concepts); Higgins, 1996 and Ratcliffe et al., 1996 (B cells); and G6bel,
1996 (T cells).
ii0
recognizing pathogen "A"can also differentiate into long-lived, fast-reacting memorycells.
Hence, during a T or B cell responseto pathogen "A", the numberof pathogen "A'specific cells increases, producinglarge numbersof pathogen "A"-specific effector cells
and memory cells. The effector cells will participatein the eliminationof pathogen "A",
whereas the memory cells will be set aside, ready to effectively respond to pathogen "A"
-
upon a repeatencounter- before pathogen"A" can cause disease. However, pathogen
"A"-specific memory cells will notprotect the individualfrom a differentpathogen (e.g.
pathogen "B"). This concept of expandingthe pool of antigen-specific cells and producing
antigen-specific memory cells is directly utilized in vaccinationprograms, whereby a nonpathogenic form of a pathogen is introduced to an individual's immune system. The
immune system will mount a response to specific components of the pathogen as described
above. Upon a later encounter with the pathogenicform of the pathogen, the immune
system will be ready to respond and eliminate the pathogen before it can cause disease.
B cells and antibodies
The B cell antigen-receptor (B cell receptoror BCR) consists of antigen-specific,
membrane-bound immunoglobulin and BCR-associated signal proteins. When a B cell
encountersthe antigen for which it has a specific BCR, it can bind to the antigen via the
BCR. The binding of the antigen to the BCR provides a first signal for B cell activation.
In most B cell-antigen interactions, the B cell requiresa second signal from T cells, in the
form of soluble factors or through direct T cell-B cell contact, before it can become fully
activated. Once activated, the B cell multipliesand differentiateseither into antibodyproducing plasmacells or memory cells. A B cell responsethat requires a second signal
from T cells is called a T-dependent response. Certainantigens, or so-called Tindependent antigens, are able to activate B cells without additional factors from T cells (Tindependent response).
Antibodies, rather than the B cell itself, are the actual effectors of the humoral
immune response. Due to their ability to specifically interact with antigen, antibodies can
greatly enhance the effectiveness of non-specificimmunecomponents. For example,
:
antibodies increase the ability of phagocytic cells to capture and eliminate antigens, activate
the complement system, and prevent antigens from binding to and infecting cells. In
chickens, three classes of antibody molecules (immunoglobulins; Ig) have been identified.
These axe IgM, IgG ClgY),and IgA.
Depending on the type and stage of a humoral immune response, different classes
of antibodies predominate. The majority of antibodies during a primary immune response
iii
are of the class IgM. A switch from IgM to IgY or IgA can be observed towards the end
of a primary immune response, however, Ig class switching to IgY or IgA is most apparent
during a second or repeated exposure to the same antigen. Additionally, different classes
of antibodies have different functional abilities. To mention a few, IgM has the ability to
easily agglutinate large antigens and to cause the precipitation of soluble antigens, thus
greatly enhancing the immune systems ability to remove antigens through phagocytosis.
IgA is found in secretions and functions at mucosal surfaces, and IgY can be transferred
from the peripheral circulation of the hen into the egg (maternal antibody).
T cell populations and_functions
Similarly to B cells, each T cell has a homogeneous set of antigen receptors (T cell
receptor; TCR) specific for a given antigen. Independent of antigen-specificity,
a T cell's
TCR can be belong to one of three classes. These are: TCR1, a heterodimer consisting of
a gamma (y) and a delta (_f)protein chain; TCR2, a heterodimer consisting of an alpha (o0
and a beta (13)protein chain which is encoded in part by a VB1 gene; and TCR3, which is
also an od3heterodimer but it's 13chain is encoded in part by a V132gene. Regardless of
which type of TCR a T cell expresses, TCR expression is always associated with a group
of signalling proteins, collectively referred to as the CD3 complex.
their TCR during thymic T cell development.
T cells first express
At this stage, most T cells already express
or start to express CD4 and CD8 cell surface molecules.
In healthy egg-type (Davidson
and Boyd, 1992) and broiler (Erf et al., 1997) chickens, double-positive (CD4+CD8 +)
lymphocytes in the thymus (thymocytes) constitute the majority of thymocytes (> 60%).
The majority of CD4+CD8 + thymoeytes express od3TCR (> 50%), a small percentage
express y_ TCR (< 10%), and the remainder do not yet express a TCR. Double-positive
thymocytes with od] TCR go through two selection processes.
First, they are selected for
their ability to recognize self major histocompatibility complex (MHC) molecules, and then
thymocytes specific for an individual's own body components are deleted or rendered
unresponsive. The majority of surviving od3TCR thymocytes will mature into
od3TCR+CD4+CD8" or od]TCR+CD4"CD8 + T cells and enter the periphery.
Minor
populations of mature od3T cells expressing both or neither CD4 and CD8 have also been
observed in the periphery (Luhtala et al., 1997; Err et al., 1997). Selection processes
regarding thymoeytes with y/5TCR (TCRI +) are less understood but do appear to exist
(Buoy et al., 1991).
Although exceptions exists, the expression of certain cell-surface molecules on T
cells are related to the T cell's functional characteristics. In chickens, as in mammals,
112
7
matureCD4+CD8 - T cells constitute the subsetof T cells which recognize exogenous
antigens (phagocytosed antigens) in association with MHC class II molecules on antigenpresenting cells (e.g. macrophages). Moreover, CD4+CD8 - T cells include the cytokineproducingregulatoryT cell subset (helperT cell) requiredfor the antigen-specific
activation of B cells, other T cells, and non-specificimmunecells (e.g. macrophages).
Mature chicken CD4-CD8+ T cells constitute the subset of T cells that recognize
endogenousantigens (viral or tumorantigens) in association with MHC class I. Once
activated, CD4-CD8 + T cells become cytotoxic, capableof the antigen-specific killing of
virus-infected cells and tumor cells. The proportionbetween CD4+CD8 - and CD4-CD8+
T cells (CD4:CD8 ratio) has been used as an end-point in assessing the state of an
individual's immune system. In chickens, the CD4:CD8 ratio has been shown to be
positively related to the amountof antibodies producedin responseto sheep red blood cells
(SRBC, a T-dependentantigen) (Parmentieret al., 1995).
Mature T cells can also be divided into subpopulationsbased on the class of TCR
they express. In young, healthy egg-type (Chertet al., 1991) and broiler (Eft et al., 1997)
chickens, TCR1+, TCR2+, and TCR3+ T cells make up 15-30%, 45-55% and 10-15%
of lymphocytes in the blood and 15-35%, 30-40%, and 10-20% of lymphocytes in the
spleen, respectively. TCR defined T cell populationsdiffer in tissue locatibn, with orbT
cells (TCR2+ and TCR3+) preferentiallyhomingto the white pulp area in the spleen,
whereas, TCR1+ T cells are most abundantwithin the red pulpof this organ. Unlike
TCR1+ and TCR2+ T cells, TCR3+ T cells are rarely found within the gut
microenvironment. Typically, matureT cells that express CD4 or CD8 also express TCR2
or TCR3. However, CD8 molecules may also be found on TCR1+ T cells, depending on
the cell's peripherallocation (e.g. spleen, IEL; Bucy et al., 1991). Lastly, TCR defined T
cell subpopulationsappearto differ in their functional capacities. For example, as shown
by Cihaket al. (1991), selective in rive depletionof TCR2+ T cells resultedin severe IgA
deficiency. Hence, TCR2+ T cells appearto be requiredfor the immunoglobulinisotype
switch from IgM to IgA and/or the expansionof IgA-producingB cells. The physiological
role of T cells expressingTCR1 is not well defined at this time.
Althoughfunctional differenceswithin the TCR defined T cell subsets are not
:
completely understood, T cells expressing TCR1, TCR2, or TCR3 nevertheless constitute
different subsets of T cells, and may constitute a diagnostic tool to assess immunesystem
state.
113
!
Aspects of Immune Development and Function in Commercial Broilers
Compared to literature on the immune system in egg-type chickens, data
specifically addressing immune development and function in broilers are limited.
Research
focus on commercial egg-type chickens may be driven, in part, by the relatively long life
of layers, requiring health maintenance from the time of hatch throughout egg-production.
Commercial broilers, on the other hand, go to market often before they are 7 weeks of
age. The short life of commercial broilers has, to some extent, taken away interest in
studying immune development and function in this type of chicken.
completely ignores the broiler breeder side of broiler production.
This of course,
However, recently,
Qureshi and Havenstein (1994) examined aspects of non-specific immunity in the 1991
Arbor Acres feather-sexable broiler strain and the 1957 Athens-Canadian Randombred
control strain (meat-type chicken).
Examination of macrophage function and natural killer
cell activity revealed little or no differences between the 1957 and 1991 strains of chickens,
suggesting that genetic selection for enhanced growth performance traits had not
significantly altered the non-specific arm of the immune system in broilers. However,
when 1957 and 1991 chicks were injected with SRBC at two-weeks of age and tested for
anti-SRBC antibody levels 7 days later, the 1957 strain had higher levels of anti-SRBC
antibodies (total Ig and IgM) than the 1991 strain (Qureshi and Havenstein,
1994). At 14
days post-SRBC injection, these strain differences in anti-SRBC antibody levels were no
longer apparent.
This drop in responsiveness to a T-dependent antigen in the 1991 broiler
strain as compared to the 1957 strain appears to be the direct result of genetic selection for
enhanced growth performance traits (Qureshi and Havenstein, 1994). The impact of this
reduction in humoral immune function on the overall livability of broilers may be
significant, as 2- to 3-week-old chicks are not fully immunocompetent and have also lost
protection from maternal antibodies (McCorkle and Glick, 1980; Peleg et al., 1985;
Pitcovski et al., 1987).
On the other hand, the modern broiler was found to have a superior ability to
produce anti-SRBC antibodies when compared to a strain of meat-type chickens which have
been solely selected on the basis of increased body weight for 36 generations (Praharaj et
al., 1995). The incorporation of immune performance as a selection criterion within a
breeding program for growth performance traits therefore appears to have beneficial
effects.
Moreover, the selection of broiler chicks for early immune response to E. coli was
shown to result in an overall increase in early immune system maturation, including 1)
increased humoral immune response to other T-dependent antigens (e.g. SRBC or bovine
114
°
serum albumin), 2) enhanced in vitro T cell proliferation in response to E. coli or T cell
mitogens, and 3) increased phagocytic activity (I-Idler et al., 1992).
Information concerning cell-mediated immunity in modern commercial broilers is
sparse. Recently, we conducted a study involving SPF Single Comb White Leghorn
(SCWL) chickens and commercial broilers raised in Anderson isolators 0aiocontainment
=
level P2). Although the intent of the study was not to compare SCWL and broilers, data
from the experimental controls can be used to gain insight into differences between
chickens that were selected for egg-production traits as compared to growth performance
traits.
In this study, blood was collected from 12 to 15 chicks per strain when the chicks
were 1, 2, and 4 weeks of age. The chicks then were euthanized, body weight was
determined, and thymus, bursa, and spleen were collected.
The weight of the bursa and
spleen was also determined for each bird. Cell-suspensions from the thymus, spleen, and
blood were immunofluorescently stained to detect the expression of CD4 and/or CD8
molecules.
The percentage of cells in each cell suspension expressing CD4 and/or CD8
was determined using a flow cytometer (FACSort, Becton Dickinson Immunocytometry
Systems, San Jose, CA).
When adjustments for body weight (BW) differences were made, the SCWL chicks
had higher bursal weights (mg/g BW) at all ages (Figure la) and higher spleen weights
(mg/g BW) at 4 weeks of age (Figure lb) as compared to age-matched broilers.
The
proportions among CD4 and/or CD8 defined T cell populations in the thymus were not
different at 1 or 2 weeks of age in SCWL and broilers (Table 1). However, by 4 weeks of
age, the broilers had a lower percentage of double-positive (CD4 +CD8 +) thymocytes and
a higher percentage of CD4-CD8 + thymocytes than the SCWL chicks.
Spleens from the
broilers consistently contained a lower percentage of CD4+CD8 - T cells than those from
SCWL chickens, whereas no strain differences were observed in the percentages of CD4CD8 + and CD4+CD8 + T ceils (Table 2). In the peripheral blood, the percentages of
CD4 +CDS" T cells were lower in 2-week-old broilers than inage-matched
SCWL chicks,
whereas the percentages of CD4-CD8 + T cells were the same between broilers and SCWL
chickens (Table 3).
Determination of CD4:CD8 ratios revealed differences between SCWL and broilers
consistent with those observed when the percentage of CD4 and/or CD8 defined T cell
subsets were examined (Figure 2). These data show that selection for egg production
versus growth performance traits has altered the proportions among T cell subsets.
Considering the different functional abilities of CD4 + CDS- and CD4-CD8 + T cells
(regulatory versus cytotoxic), the strain differences observed here likely reflect differences
in the general immunocompetence of SCWL as compared to broilers.
115
For example, low
CD4:CD8 ratios have been associated with lower antibody responses to SRBC and higher
body weights (Parmentier et al., 1995). Hence, based on the data presented above,
broilers would appear to be less immunocompetent than SCWL chickens during their first 4
weeks of life. The conclusion that young broilers have below optimal immune system
function is further corroborated by the observation that management practices can
positively influence a broiler's immune state. For example, dietary vitamin E (c_tocopherol) supplementation at levels 5 to 10 times above standard levels was found to
significantly increase the CD4:CD8 ratios in thymus, blood, and spleen in broilers raised
on litter (Erf and Bottje, 1996). The enhanced CD4:CD8 ratio in the blood was associated
with increases in the ability of lymphocytes to respond to T cell mitogen and in the
antibody response to a T-independent antigen (S. pullonvn) (Eft and Bottje, 1996).
More information is needed regarding immune development and function in
broilers.
This information will be valuable in identifying selection criteria at the pedigree
level to improve future commercial broiler performance.
Until the genetic immune system
potential has increased, better immune system development and function in broiler chicks
can be achieved through optimizing nutritional and environmental conditions.
Acknowledgments
The excellent technical help provided by Tina Bersi, Chris Fritts, and Belinda Floyd is
very much appreciated.
This manuscript is published with the approval of the Director of
the Arkansas Agriculture Experiment Station, University of Arkansas.
This work was
supported, in part, by a grant from the US Poultry and Egg Association (Tucker, GA).
References
Bucy, R.P., Chert, C.-L.H. and Cooper, M.D., 1991. Analysis ofy_ T cells in the
chicken. Sem. Immunol., 3: 109-117.
Chen, C.-L.H., Pickel, J.M., Lahti, J.M. and Cooper, M.D., 1991. Surface markers on
avian immune cells. In: J.M. Sharma (Editor), Avian Cellular Immunology, CRC
Press, Boca Raton, FL, pp. 1-22.
Cihak, J., Hoffmann-Fezer,
C.-L.H.,
G., Ziegler-Heibrock,
H.W.L., Stein, H., Kaspers, B., Chen,
Cooper, M.D. and Ltsch, U., 1991. T cells expressing the .VB1T-cell
116
°
receptor are required for IgA production in chicken.
10951-10955.
Proc. Natl. Acad. Sci., 88:
Davidson, N.J. and Boyd, R.L., 1992. Delineation of chicken thymocytes by CD3-TCR
complex, CD4 and CD8 antigen expression reveals phylogenicaUy conserved and
novel thymocyte subsets. Int. Immunol., 4:1175-1182.
"
Davison, T.F., Morris, T.R. and Payne, L.N., 1996. Poultry Immunology.
Poultry
Science Symposium Series, Vol.24, Carfax Publishing Company, Abingdon,
England.
Erf, G.F. and Bottje, W.G., 1996. Nutrition and immune function in chickens: Benefits
of dietary vitamin E supplementation.
Proceedings of the Arkansas Nutrition
Conference, pp. 113-130.
Err, G.F., Bottje, W.G. and Bersi, T.K., 1997. CD4, CD8, and TCR defined T cell
subsets in thymus and spleen of 2- and 7-week-old commercial broiler chickens.
Vet. Immunol. Immunopathol. (submitted).
G6bel, T.W.F.,
1996. The T-dependent immune system. In: T.F. Davison, T.R. Morris
and L.N. Payne (Editors), Poultry Immunology, Poultry Science Symposium Series
Vol.24, Carfax Publishing Company, Abingdon, England, pp. 31-45.
Han, P.F.-S. and Smyth, J.R., Jr., 1972. The influence of growth rate on the
development of Marek's disease in chickens. Poultry Sci., 51: 975-985.
Heller, E.D., Leitner, G., Friedman, A., Uni, Z., Gutman, M. and Cahaner, A., 1992.
Immunological parameters in meat-type chicken lines divergently selected by
antibody response to Escherichia coli vaccination. Vet. Immunol. Immunopathol.,
34: 159-172.
Higgins, D.A., 1996. Comparative immunology in avian species. In: T.F. Davison, T.R.
Morris and L.N. Payne (Editors), Poultry Immunology, Poultry Science
Symposium Series, Vol.24, Carfax Publishing Company, Abingdon, England, pp.
149-205.
Luhtala, M., Lassila, O., Toivanen, P. and Vainio, O., 1997. A novel CD4+CD8
+ T
cell population: inheritance of CDSot expression on CD4 + T cells. Eur. J.
Immunol., 27: 189-193.
.
McCorkle, F.M. and Glick, B., 1980. The effect of aging on immune competence in the
chicken: antibody mediated immunity.
Poultry Sci., 59: 669-672.
Parmentier, H.K., Kreukniet, M.B., Goeree, B., Davison, T.F., Jeurissen, S.H.M.,
Harmsen, E.G.M. and Nieuwland, M.G.B., 1995. Differences in distribution of
lymphocyte antigens in chicken lines divergently selected for antibody responses to
sheep red blood cells.
Vet. Immunol. Immunopathol.,
t17
48: 155-168.
Parmentier, H.K., Nieuwland, M.G.B., Rijke, E., De Vries Reilingh, G. and Schrama,
J.W., 1996. Divergent antibody responses to vaccines and divergent body weights
of chicken lines selected for high and low humoral responsiveness to sheep red
blood cells. Avian Dis., 40: 634-644.
Peleg, B.A., Heller, D.E. and Pitcovski, J., 1985. The ontogeny of the humoral response
to Escherichia coli vaccine and to sheep red blood cells in young chicks. Avian
Pathol., 14: 471-481.
Pitcovski, J., Heller, D.E., Cahaner, A. and Peleg, B.A., 1987. Selection for early
responsiveness of chicks to Escherichia coli and Newcastle disease virus.
Poultry
Sci., 66: 1276-1282.
Praharaj, N.K., Dunnington, E.A. and Siegel, P.B., 1995. Growth,
immunoresponsiveness,
and disease resistance of diverse stocks of chickens reared
under two nutritional regimens.
Poultry Sci., 74: 1721-1729.
Qureshi, M.A. and Havenstein, G.B., 1994. A comparison of the immune performance of
a 1991 commercial broiler with a 1957 randombred strain when fed typical 1957
and 1991 broiler diets. Poultry Sci., 73: 1805-1812.
Ratcliffe, M.J.H.,
Paramithiotis, E., Coumidis, A., Sayegh, C., Demaries, S., Martinez,
O. and Jacobsen, K.A., 1996. The bursa of Fabricius and its role in avian B
lymphocyte development. In: T.F. Davison, T.R. Morris and L.N. Payne
(Editors), Poultry Immunology, Poultry Science Symposium Series, Vol.24, Carfax
Publishing Company, Abingdon, England, pp. 11-30.
118
Table 1. CD4 and CD8 Defined Lymphocyte
Subsets (%) in Thymus from SCWL and
Broiler Chicks Reared in Isolation
Strain Age
CD4
CD8
CD48
SCWL
Broiler
1 wk
1 wk
8.0 4- 1.1
5.7 4- 0.9
5.9 4- 0.7
4.5 4- 0.4
92.8 4- 1.0
89.6 + 2.2
SCWL
Broiler
2 wk
2 wk
9.2 4- 1.4
9.9 4- 1.4
7.3 4- 1.5
13.2 4-3.1
81.4 4- 5.4
70.9 4- 6.3
SCWL
Broiler
4 wk
4 wk
6.7 4- 0.7
7.9 4- 1.0
5.6 4- 0.7b
7.5 4- 0.6a
80.1 4-2.3a
72.4 4- 2.5b
Data shown are mean % + SEM.
See legend Fig. 2 for experimental detail.
a,bWithin a cell type and an age group, means with different
superscripts are significantly different (P < 0.05).
Table 2. CD4 and CD8 Defined Lymphocyte
Subsets (%) in Spleen from SCWL and
Broiler Chicks Reared in Isolation
-
Strain
Age
SCWL
Broiler
1 wk
1 wk
SCWL
Broiler
SCWL
Broiler
CD4
CD8
CD48
20.0 4-0.9a
14.5 4- 1.5b
23.2 4- 1.5
26.2 4- 1.8
2.3 4- 0.3
2.1 4- 0.4
2 wk
2 wk
15.5 4- 1.5a
11.2 4-0.5b
29.3 4- 4.6
29.0 4-3.3
3.9 4- 0.7
2.6 4- 0.5
4wk
4wk
14.3 4- 1.0a
10.9 4- 0.9b
32.1 4- 1.7
36.4 4- 2.5
5.2 4- 0.8
3.7 4- 0.6
Data shown are mean % + SEM;
See legend Fig. 2 for experimental detail.
a,bwithin a cell type and an age group, means with different
superscripts are significantly different (P < 0.05).
119
Table 3. CD4 and CD8 Defined Lymphocyte
Subsets (%) in Blood from SCWL and Broiler
Chicks Reared in Isolation
Strain
Age
CD4
CD8
CD48
SCWL
Broiler
1 wk
1 wk
43.9± 3.4
42.9 4- 2.6
15.0± 1.0
15.8 4, 1.8
1.4 4-0.2
2.0 4, 0.3
SCWL
Broiler
2 wk
2 wk
51.2 4-2.4a
27.6 4- 2.9b
17.54- 1.1
17.4 4- 2.5
1.64, 0.2a
0.3 4- 0.1b
SCWL
Broiler
4 wk
4 wk
21.6 4- 2.8
19.7 4, 1.9
9.6 4- 1.7
8.8 4- 0.8
1.54- 0.2a
0.7 4- 0.2b
Data shown are mean % + SEM;
See legend Fig.2 for experimental detail.
a,bwithin a ceil type and an age group, means with
different superscripts are different (P < 0.05).
120
O.
r
SCWL
Broiler
Figure 1.
Bursa (a) and spleen (b) weights in specific pathogen free
Single Comb White Leghorn (SCWL) and commercial
broiler chicks raised in isolation (biocontainment level 2).
At 1, 2, and 4 weeks of age, the bursa and spleen were
removed from 12 to 15 birds per strain. Bursa and spleen
weights were determined and adjusted for body weight (BW)
differences.
Ig
Indicates significant strain differences within an age-group
(P < 0.05).
121
3.5
3
-
2.5
2
Q1 wk
_
m2 wk
1
114 wk
0.5
0
S
Thymus
B
S
B
Spleen
S
B
Blood
Figure 2.
Proportions between CD4 + CD8" and CD4-CD8 + T cells
(CD4:CD8 ratio) in thymus, spleen, and blood from specific
pathogen free Single Comb White Leghorn (SCWL) and
commercial broiler chicks raised in isolation (biocontainment
level 2). At 1, 2, and 4 weeks of age, the thymus, spleen,
and blood were obtained from 12 to 15 birds per strain.
Cell suspensions were immunofluorescently stained using
monoclonal antibody specific for chicken CD4 (FITClabeled) and CD8 (PE-labeled) and a two-color, direct
staining procedure. The percentage of cells expressing CD4
and/or CD8 was determined by flow cytometry.
*Indicates significant strain differences within a tissue type
and an age group (P < 0.05).
122
Questions
Question: S. J. Lamont
Many past studies have compared distinct populations, and have found a negative
•
relationship of body weight and immune function. Have you examined the
"
relationship of body weight and immune parameters within the population that you
have studied?
Response: G. F. Erf
No I have not. Healthy commercial broilers examined in our laboratory had
relatively uniform body weights. Hence, it will be difficult to establish a
relationship between body weight and immune function within a population of
healthy broilers. Another approach used to determine the relationship between
body weight and immune function was to divergently select a population of
chickens for high or low immunocompetence (e.g." H. K. Parmentier and coworkers; P. B. Siegel and co-workers). Using this approach, it was demonstrated
that selection of chickens for high or low antibody titers tOsheep red blood cells
resulted in lower and higher body weights, respectively, as compared to randombred controls.
Question: M. Boyle
Can you envision using a flow cytometer on an industrial level (i.e. large numbers
of samples)? How much does the machine cost?
Response: G. F. Erf
Yes I can. A basic flow cytometer, equipped with a single argon laser (488 nm)
and three fluorescence detectors, can simultaneously provide information about
size, internal complexity, and fluorescence (up to three different fluorescent labels)
of a single particle (e.g. cell). It can perform these tasks at high speed (10,000
particles in less than 5 seconds). Hence, a large number of samples can be
processed in a day. Various diagnostic kits are currently being developed for
,
poultry species requiring the use of a flow cytometer.
•
the capabilities described above will cost between $80,000 to $100,000.
service contract will be between $10,000 to $15,000 a year.
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A basic flow cytometer, with
The