Download Lung Host Defenses: A Status

their activation can occur with nonspec%c/nonimmune
stimuli. With the exception of immunoglobulins with
specific antibody activity, these surveillance mechanisms
are not dependent on the immune status of the host. In
contrast, other augmenting mechanisms are built into the
lung defense which enhance the responsiveness of the
system and make it flexible and adaptable. These will be
discussed in more detail.
The first augmenting mechanism is the lung's ability
to mount immune responses (humoral and cellular) to a
variety of antigenic stimuli which bombard the organ. As
yet, these immune responses are not well understood nor
precisely localized within the respiratory tract. The importance of dissecting these responses is obvious-to
make subsequent immunization protocols more specific
and effective for the respiratory system. Foreign substances, be they inhaled exogenous micmrganisms and
environmental antigens, or altered body proteins and
cellular emboli which traverse the intravascular route,
reach the airways or the lung vasculature in several
ways. Inhalation of particulates in inspired ambient air is
perhaps the most important way. Aspiration of
oropharyngeal contents, generally associated with a state
of diminished consciousness or with impaired function of
hypopharyngeal structures, can occur in normal people,
often during sleep. From the vascular direction, the
venous circulation carries innumerable substances and
particulates to the right side of the heart and ultimately
into the lung parenchyma. Because the lung in normal
subjects receives practically an of the blood flow, its
capillary network is the most extensive in-line filter in
the body. Thus, it seems reasonable that immune responses can have their origin from either the air side or
the vascular side of the lung. The relative importance or
balance between the two response pathways is unclear
at present.
First, examining immune responses which originate
from the air side, the disposal of antigens entering the
airways must be an extraordinarily efficient process. De-
Lung Host Defenses: A Status
~e~ort*
Herbert Y . Reynolds, M.D., F.C.CJ.
o perform its task of air-exchange adequately, the
Trespiratory
system must recognize and eliminate the
many unwanted elements in inspired air such as particulates, noxious gases, microbes and other contaminants.
This nonrespiratory activity of purifying inspired air and
keeping lung tissues free of infection has been collectively termed "lung host-defense mechanisms." There has
been considerable interest in this aspect of lung function
in the past ten years or so; a number of recent publicationsl-lo review the subject in detail. As a result, the
major components of lung defense have been identified
and dissected appropriately. Whereas the ingredients of
lung defense are well described, less is known about the
coordination of the parts or integrated function of the
whole defense apparatus. Current research efforts seem
to be focusing on these latter areas, especially on cellular
interactions, generation of local lung immune responses,
and amplifying-inhibitory factors regulating idammation. Study of such interactions is important because
most are being conducted at a fundamental enough level
that molecular manipulation seems promising, and
hence, the potential for clinical control of many lung
diseases appears possible. This review will stress these
latter interactions.
Elements of the defense system are spaced along the
entire respiratory tract from the point of air intake at the
nares to the level of oxygen uptake on the alveolar
surface (Table 1). In the conducting airways, which
functionally begin in the nose and extend to the respiratory bronchioles, anatomic bamers, branching of the
respiratory tree, mucus entrapment and ciliary clearance, the cougb response, bronchoconstriction, and local,
mucosally derived proteins (such as secretory IgA) aIl
act mechanically to exclude or clear particulate material
from the respiratory tract. Distal to the respiratory bronchioles in the air-exchange units, other elements become
more important and take charge. Lining material of the
alveoli (surfactant ) ; iron-con taining proteins (transferrin); other immunoglobulins (such as I&); and
properidin B, which can trigger the alternate pathway of
complement activation, all have varying activity against
inhaled particles or microorganisms. Finally, there loom
the alveolar macrophages, the principal phagocytic cells
in the airways and scavenger of the alveolar surfaces. All
of these things are operant in the normal human respiratory tract and might be categorized as on-going surveillance mechanisms. Their function is either mechanical or
the Pulmonary Section, Department of Medicine,
Yale University School of Medicine, New Haven
Supported by NIH Grant HL-22302and Grant 1197,Corncil for Tobacco Research, Inc.
Reprint requests: Dr. Reynolds, Y& Unioers#y School of
Medicine. 333 Cedar Street, New Haven 06510
Table 1-AngHast Defen8es to A i m C h d e n g e
Surveillance Mechanisms
Mechanical barriers and airway angulation
Lymphoid tissue
Mucociliary clearance
cough
Bronchoconstriction
Local immunoglobulin coating--secretory IgA
Other immunoglobulin clssses (IgG, IgE)
Fe-containingproteins (tnmsferrin)
Alternate complement pathway activation
Surfactant
Alveolar macrophages
O h m
CHEST, 75: 2, FEBRUARY, 1979 SUPPLEMENT
.
Augmenting Mechanimns
Initiation of immune responses (humoral antibody and
dular)
Generation of an inflammatory response (influx of polymorphonuclear granulocytes, eosinophils, and ? lymphocytes)
IMMUNOLOGY OF THE LUNG 238
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pending upon particle size, larger insoluble substances
and particulates impact in the nose ( > 10 P diameter)
or at points along the trachea and conducting airways
( < 10 p to 3-5 p diameter) ;smaller particles (0.5 p to 3
p) may reach the alveolar surface.. Whereas insoluble
antigens that adhere to mucosal surfaces are likely
cleared by combined mucociliary action and coughing,
those that are in part soluble may be absorbed across the
mucosal surface. The fate of such abcPorbed antigens may
be decided in the general circulation and organs of
systemic immunity. Increased permeability of the mucosa does not account for allergic (atopic) individuals
having an enhanced IgE antibody response to inhaled
allergens. Certainly, the integrity of the epithelial mucosal surface appears crucial in determining patterns of
bacterial adherence and colonization in the upper respiratory tract. Poor nutrition, which may alter sugar surface receptors of buccal epithelial cells, inadequate
amounts of secretory IgA antihdy, or presence of IgA
proteases elaborated by certain bacteria can promote
preferential sticking of certain bacteria and explains
colonization.
Interaction between inhaled antigens and lymphoid
tissues spaced along the respiratory tract seems quite
probable from an anatomic standpoint, yet relatively
little information is available to substantiate this idea.
There is extensive fmed lymphoid tissue in the nasooropharynx (WaMeyer's ring) p h more d-ly
distributed bronchus-associated lymphoid tissue (BALT)
found in the trachea and bronchi. BALT seems strategically located to intercept antigens which impact at
branching points in the conducting airways. Recent
work in immunized rabbits" has shown antigen uptake
in the specialized lympho-epithelium imply@gthat antigen trapping does occur. In pertinent human stdies,
Clancy and colleagues1* have shown that BALT is
immunoreactive in its recan of common antigens; What
actually initiates de nooo an immune response is still
largely unknown. Several interesting possibilities are
present. First, BALT contains relatively more B-lyrnphocytes than T-cells and a large percentage of non-surface
reactive lymphocytes called ''null" cells. Admittedly, one
must be careful in interpreting the huge null ceU percentage, because inability to identify or sub-populate
these lymphocytes may reflect insensitivity or limitation
of currently used immune complex reagents. Second, it
appears that BALT is a repository for potentially immunoglobulin-secreting cells, particularly IgA cells.
Bienenstocks has speculated that other immunoglobulinsecreting cells may have their origin here as well ( IgG
and IgE) . Third, such immunoglobulin-secreting (antibody-producing) cells can traffic to the lamina propria
along the respiratory tract and produce local antibody
which coats mucosal surfaces. Fourth, it is conceivable
that lung tissue mast cells and basophils emanate from
BALT sites3 Such cells, which liberate various mediators of acute allergy (type 1 reactions) following stimulation of surface-bound IgE antibody, could implement
BALT in the development of allergic immune responses
in the lungs. As yet, this is u n b e d . What happens
to antigen-primed or stimulated lymphocytes after they
leave BALT is uncertain. A local circuit into the s u b
mucosa of the lung is only one route. How (or if) such
lymphocytes reach lymph node tissue in the lungs (hilar
nodes) or systemic nodal structures is unclear. Technically, the BALT system is dif6cult to work with, certainly difficult compared to Peyer's patches (gut-associated lymphoid tissue) with which BALT is usually
compared. Whereas BALT and Peyer's patches are
ostensibly similar morphologically, functionally there
may be merences. For instance, in studying the kinetics
of Peyer's patch immunization in Lewis rats Levin and
colleagues's found little antigen-specific lymphocyte
stimulation in Peyer's patches themselves, but found it in
the draining mesenteric lymph nodes instead. This
would suggest in the gut that lymphocyte differentiation
occurs at a more distal site in the afferent limb and not
within the Peyer's patch. In the lung, the implication is
that such B-lymphocyte differentiation may occur wholly
within the BALT structure. However, BALT does not
contain plasma cells; therefore, some differentiation of
antibody producing cells must occur outside BALT.
Other distal lymphoid collections may also interact with
antigens. Lymphoid aggregates located at the respiratory bronchiole-alveolar (terminal lung units) junction
are well situated for exposure to inhaled antigens. Finally, free lymphocytes, usually retrieved from peripheral
airways by lung lavage, exist. These cells consist of both
&(bursa1 derived) lymphocytes and T (thymus derived) lymphocytes and are present in ratios that approximate those found in peripheral blood.
Airway antigens that reach the terminal air-exchange
d a c e of the alveolar units have a different fate. Two
possibilities seem likely. First, alveolar macrophages intercept and then process or degrade the antigen; these
phagocytes eventually exit the lung via the mucociliary
escalator6 and are expectorated, or antigen-containing
macrophages leave the alveolar surface and migrate
through the interstitium to lymphatic channels which
carry them to regional lymph nodes. Second, antigen
may be absorbed directly from the alveolar surface and
eventually gain access to lymphatic channels which
eventually empty into regional lymph nodes. Recently,
Kaltreider and associate^^-^ have investigated the response of sheep red blood cell antigens (SRBC) instilled
into the lower respiratory tract of dogs. Such an inflarnmatory-antigen stimulus elicits antibody forming cells
(AFC)in alveolar exudates, as well as in draining hilar
lymph nodes. This route of immunization provides a
minimal systemic response (ie in peripheral nodes or
spleen), but there is some antigen spill-over which is
more evident upon a second exposure of antigen. An
important point to recognize is that practically all of the
instilled alveolar antigen is phagocytosed and carried by
alveolar macrophages and other idammatory cells to
the draining lymph nodes; little if any "free" antigen
escapes from the lung despite large immunizing doses.
Antigens, soluble or particulate, may come to the lung
parenchyma by way of the circulatory route and lodge in
some portion of the lung vasculature. For conceptual
CHEST, 75: 2, FEBRUARY, 1979 SUPPLEMENT
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purposes, let us limit antigen localization to the capiflary
network which places it in proximity to the alveolar
surface. At this point, the capinary endothelium traps
antigens which either can gain access to the lung parenchyma or eventually pass through to the general circulation. Intravenous immunization generally produces a
disproportionally large antibody-response in spleen,
lymph nodes and systemic immune organs and relatively
little response in lung. However, some antibody responsive cells ( AFC) have been retrieved in bronchoalveolar
lavage and in hilar lymph nodes of dogs following IV
immunization with SRBC.' Changes in local permeability of the lung capillaries would facilitate the absorption
of antigen into interstitial spaces and start it dong a
pathway which leads to lymphatic vessels which eventually drain into hilar lymph nodes. Along the way,
antigen could encounter interstitially located macrophages which pick it up. The relative balance, then,
between the direction antigen takes after it lodges in the
vasculature is determined by the degree of local irritation and changes in permeability that antigen evokes.
This probably dictates the relative load of antigen presented to the lung and may correlate with the immune
response the lung subsequently mounts.
The surveillance mechanisms (Table 1)usually suffice
to insure ainvay sterility or to protect against the challenge of microorganisms and other antigens. However,
the potential to readily mount an inflammatory response
in lung parenchyma represents a potent back-up mechanism. h~this respect, the second augmenting mechanism,
the idammatory response, can be perceived as a controlled reaction that requires specific initiation, modulation and ultimately dissolution. The immune status of the
host (T-lymphocyte hypersensitivity, presence of agglutinating and opsonic antibody or activated maphages) may help to accelerate the development of the
inflammatory process; likewise, these same factors can be
deleterious as well by destroying lung tissue in some
circumstances. Research directed to dissecting the inflammatory response relies heavily on uncovering cell-tocell signals which regulate and promote cellular interactions. Increasingly, the alveolar macrophage appears to
be a critical modulating cell. Its central position on the
alveolar surfaces as the phagocytic front line, makes this
pivotal role reasonable. To examine this inflammatory
reaction, a bacterial example is an easy one to visualize.
As mentioned, opsonic antibody (IgG via an Fcr e
ceptor) , complement factors (Cab), and possibly surfactant can specifically attach bacteria to macrophage
membrane surfaces. Stimulated lymphocytes can release
mediators (lymphokines) such as migration inhibition
factor or macrophage activating factor which alter
macrophage movement or increase membrane motion.
All of these may enhance macrophage phagocytosis and/
or intracellular killing. At what point the alveolar macrophage senses that it is ovenvhehned and needs additional phagocytic help is unlcnown. One suspects that a
large bacterial inoculum or particularly virulent microorganisms may be factors. Whatever the sensing mechanism, the alveolar macrophage has a large m y of
CHEST, 75: 2, FEBRUARY, 1979 SUPPLEMENT
secretory substances to throw into the fray. The macrophage can produce several secretory substances which
have chemo-attractant activity and can cause directed
movement of other inflammatory cells-PMNs, eosinophils, and possibly lymphocytes. At least two macrophagederived factors, C, (activated as C,a) and a
smaller molecular weight molecule (- 2,000 d ) are
very active in d r o in promoting transfilter migration of
PMNs. Although aggregated IgG or immune complexes
are the most potent stimuli of chemotactic release from
macrophages, nonspecific release mechanisms occur as
well, since contact adherence of macrophages to glass
surfaces can also promote significant factor release. Other
macrophage-derived factors such as plasminogen activator may be active, too. In some way, PMNs are recruited
to the alveoli and an inflammatory exudate develops.
Once PMNs have entered the alveoli, they can perpetuate their influx by self-generating C,a. One ingredient ignored in the above sequence is some sort of
permeability factor which accounts for the accumulation
of fluid which accompanies the cellular influx into alveoli.
A vasoactive peptide of the kallikrein system may be a
candidate. In uiuo, the kinetics of this response may
require up to 24 hrs for completion. With successful
containment of the microorganisms, the inflammatory
process should subside. Resolution is also an active process that is initiated by other factors such as "chemotactic inhibition factor" from the serum14or C,a enzyme
cleaving enzyme, etc. Macrophages are again important
in this phase of clean-up. Eventually, nofind lung architecture is restored as the exudate clears.
In conclusion, the lung defenses are remarkably efficient in protecting against infections and other respiratory diseases caused by harmful substances or gases in
inhaled air, considering the burden of daily exposure
versus the rarity of respiratory illness. Collectively, the
elements of the defense system work smoothly and tirelessly. Increasingly, however, examples of isolated
immune deficiencies are being found which are associated with recurrent pulmonary infections. Complement factor deficiencies ( C,) , abnormally functioning
cilia (Kartagener's syndrome), absence of immunoglobulin (IgA), and abnormal leukocytes, all predispose to
lung infections. A single ddciency in itself may not
predispose to overwhelming lung infections. This attests
to the flexibility of the host defense apparatus in that
compensating mechanisms can evolve. Whereas the selective deficiencies serve as splendid probes for assessing
the importance of individual components in lung defense, their absence also dramatizes the adaptability of
lung defenses as well.
1 Green GM: The J Burns Amberson Lecture-In defense
of the lung. Am Rev Respir Dis 1@2:691-703,1970
2 Cohen AB, Gold WM: Defense mechanisms of the lungs.
An Rev Physio137:325-350,1975
3 Bienenstodc J, Clancy RL, Percy DYE: Bronchus associated lymphoid tissue (BALT): its relationship to
m u d immunity. Immunologic and Infectious Reactions
in the Lung (Kirkpatrick CH, Reynolds HY, eds) Basel
IMMUNOLOGY OF THE LUNG 241
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and New York, M. Dekker, Inc, 1976, pp 29-58
4 Kaltreider BH: Expression of immune mechanisms in the
lung. Am Rev Respir Dis 113:347-379,1976
5 Newhouse M, Sanchis J, B i e d J: Lung defense
mechanisms. N Engl J Med 295:sSe997, 1045-1052,
1976
6 Green GM, Jakab CJ, Low RB, et al: Defense mechanisms of the respiratory membntne. Am Rev Respir Dis
115:479-514, 1977
7 Kazmierowski JA, Aduan RP, ReywMs HY: Puhnonary
host defense: Coordinated mteraction of mechanical, cellular and humoral immune systems of the lung. Bull
Europ Physiopath Resp 13:103-116,1977
8 Breeze RG, Wheeldon EB: The cells of the p u h n w
airways. Am Rev Resp Dis 116705-777, 1977
9 Respiratory Defense Mechanisms (Part I, 11) (Brain JD,
Proctor DF, Reid LM, eds) Basel and New York, M.
Deklter, 1977
~
mechanisms. In
10 Johanson WC, Gould KC: L M defense
Basics of RD. New Yo*, American Thoracic Society,6: 1-
6, 19T7
11 Racz P, Tenner-Racz K, Myrvik QN, et al: Functional
architure: Bronchial associated lymphoid tissue and lymphoepitheliwn in puhnonary cell-mediated reactions in
the rabbit. J Reticnol Soc e2:59-83,1977
12 Clancy RL,Pucci AA, Jelihovsky T, et al: Immunologic
"memory" for microbial antigens in lymphocytes obtained
Am Rev Respir Dis
from human bronchus mu117:513518,1978
13 Levin DM, Ottesen EA, Reynolds HY et al: Cellular
immunity in Peyerb patches of rats infected with TrichG
n e b spimlis. Infect Imrnunol13:2730,1976
14 Berenberg JL,Ward PA: The chemotactic factor inactivator m normal human serum. J Clin Invest 52:1UW)1208,1973
Impairment of Pulmonary
Antibacterial Defense Mechanisms
by Halothane ~nesthesia*
Bingumal R. Munawudu, M.D., und F.
M m LaForce, M.D.
P"
onary antibacterial defenses include aerodynamic filtration, physical clearance of inhaled or
aspirated organisms by the mumdiary escalator system,
and phagocytosis by alveolar macrophages. These
mechanisms maintain sterility of distal lung tissue despite inhalation of potential microbes.
Pulmonary infections postoperation are more common
after use of inhalation anesthesia when compared to
spinal anesthesia. This increased incidence has generaJly
been attributed to aspiration, retention of bronchopulmonary secretions, and occasionally to contaminated
equipment. Important contributory factors include age
of patient, type of surgery performed, and the duration
of anesthesia.l
Because of the contact which ciliated epithelial cells
of the respiratory tract and alveolar macrophages would
-
*From the
Uni%YEEL Pad4Medicine,
Vetennr Ad-
versity
. . of
mmstration Hospital, Denver.
Reptint requests: Lk.M-adu,
Department of Anestfie8tology, 4200 East Ninth, Denoer 80262
242 2 1 ~ tASPEW LUNG COWFEREWCE
have with an inhaled anesthetic, a possible hypothesis to
explain the increased incidence of pneumonia would be
a direct, anesthesia-induced depression of lung defenses.
Thus, we investigated the effects of a commonly used
general anesthetic agent, halothane, on pulmonary antibacterial activity and ciliary activity.
Pulmonary Bactericidal Studies
Mice were anesthetized with halothane concentrations for
a period of four hours. They were then allowed to rerover
and one hour later were challenged for 30 minutes with
aerosolized P,, radiolabelled Stuphylococcus ourew. Immediately after aerosol challenge and again four hours later,
equal numbers of previously anesthetized and control mice
were killed by luxation of the neck. The lungs were aseptically removed, homogenized, serially diluted and cultured quantitatively in triplicate on petriplates
These plates were incubated and the colonies counted.
Radioactivity was measured by transferring a separate ahquot of lung homogenate into scintiIlating vials. The radioactivity was assayed in a liquid scintillation counter and
expressed as counts per minute per ml of the material
assayed. Intrapulmonary activity was determined in individual animals by comparing four-hour bacterial count/isotope
count ratios to a similar ratio determined immediately after
the aerosol exposure.
Ciliaty Activity Studies
Under strict sterile conditions, the trachea of a ferret was
dissected from below the vocal cords to the carina by blunt,
bloodless dissection, then removed, and complete rings prepared by cutting transversely between tracheal cartilages.
The rings of trachea were carefully transferred to sterile
screw-top tubes containing 1ml of Leibowitz-15 medium and
rolled on a tissue rotator in a 33OC incubator. The use of L15 medium and rolling the screw-top tubes prolonged the
survival of the ciliated epithelium beyond that obtained using
other standard media2
Under strict sterile conditions, halothane concentrations
were bubbled though the medium and the ciliary activity
was determined.2 Room air was bubbled through the control
tubes.
Groups of tubes were exposed to halothane concentrations,
1.0, 2.0, 3.0, 4.0, and 5.0 percent and ciliary activity was
determined on a daily basis for five days. All tubes were read
blindly by a single observer (BRM) and data expressed as
percentage of cilia beating. To determine the recovery of
ciliary activity, another group of culture tubes was exposed to
4 percent halothane. Every 24 hours a set of culture tubes
was exposed to air and the recovery of ciliary activity
recorded.
Intrapulmonary bactericidal activity was depressed in
both groups of anesthetized animals. At four hours, the
mice that had been anesthetized had a significantly
greater percentage of viable bacteria remaining (41.8 +
4.1 percent with one MAC halothane and 43.1
3.4
percent with two MAC halothane) when compared to
controls (29.3 + 2.3 percent; P < .02 with one MAC
halothane and 18.5 2 1.3 percent, P < .005 with two
MAC halothane). These studies demonstrated that the
alveolar macrophage function is adversely affected after
*
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