Characterization and response to mitogens of mammary lymphocytes from the bovine dry-period secretion

Effect of β-hydroxybutyric acid, parity, and body condition score on phenotype and proliferative capacity of colostral mononuclear leukocytes of high-yielding dairy cows

In neonatal calves, the ingestion of colostrum is imperative for preventing infectious diseases. Investigations into the transfer of passive immunity of cattle have primarily focused on the importance of colostral immunoglobulins, with a recent increase in focus on understanding the role of colostral leukocytes. The main objective of the present study was to measure the influence of parity, body condition score, serum nonesterified fatty acids, and serum β-hydroxybutyrate concentrations of periparturient cows on phenotype and mitogen- and antigen-induced proliferative capacity of bovine colostral leukocytes. Holstein-Friesian cows (n=141) were intramuscularly vaccinated at 60 and 30 d before the expected parturition date with a tetanus toxoid vaccine. Of these 141 animals, 28 primiparous and 72 multiparous cows were sampled immediately after parturition. Colostrum mononuclear cell populations were identified by flow cytometry using bovine cluster of differentiation markers, and the proliferative capacity of these cells was determined using a (3)H-thymidine proliferation assay. Under-conditioned cows had a significantly higher percentage of colostral macrophages than normal-conditioned animals, whereas over-conditioned cows had significantly more colostral B-lymphocytes. Serum β-hydroxybutyrate was significantly associated with higher numbers of colostral T-lymphocytes and macrophages. Heifers had significantly higher mitogen- and antigen-induced proliferation of their colostral leukocytes than third parity or older cows. In conclusion, body condition score, parity, and serum β-hydroxybutyrate concentration of periparturient high-yielding dairy cows were shown to influence the number of colostral macrophages or the mitogen- and antigen-induced proliferation of colostral leukocytes, possibly influencing the cellular immunity of the newborn calf.

The Immunology of Mammary Gland of Dairy Ruminants between Healthy and Inflammatory Conditions

The health of dairy animals, particularly the milk-producing mammary glands, is essential to the dairy industry because of the crucial hygienic and economic aspects of ensuring production of high quality milk. Due to its high prevalence, mastitis is considered the most important threat to dairy industry, due to its impacts on animal health and milk production and thus on economic benefits. The MG is protected by several defence mechanisms that prevent microbial penetration and surveillance. However, several factors can attenuate the host immune response (IR), and the possession of various virulence and resistance factors by different mastitis-causing microorganisms greatly limits immune defences and promotes establishment of intramammary infections (IMIs). A comprehensive understanding of MG immunity in both healthy and inflammatory conditions will be an important key to understand the nature of IMIs caused by specific pathogens and greatly contributes to the development of effective control methods and appropriate detection techniques. Consequently, this review aims to provide a detailed overview of antimicrobial defences in the MG under healthy and inflammatory conditions. In this sense, we will focus on pathogen-dependent variations in IRs mounted by the host during IMI and discuss the potential ramifications of these variations.

Development of a method for isolating bovine colostrum mononuclear leukocytes for phenotyping and functional studies

The present study reports a method for isolating bovine colostrum mononuclear cells (CMC) for phenotyping and functional studies. As well as being an important source of immunoglobulins, colostrum also contains leukocytes that may be of greater importance for passive immunity than has previously been thought. Different protocols have been reported for isolating leukocytes from bovine colostrum, although none of these have been validated, and phenotypic analysis of cell populations has not always been performed. In this study, bovine CMC were isolated by density gradient centrifugation. Cell populations were identified by flow cytometry using antibodies against selected bovine cell surface markers and the proliferative capacity of these cells was determined using a (3)H-thymidine proliferation assay. The mean cell count of isolated CMC was 3 × 10(4) and 1 × 10(5) per mL colostrum for the samples used in the flow cytometric assay and the proliferation assay, respectively. A mean of 25.4 ± 17.1% CMC were identified as T lymphocytes, 2.9 ± 3.0% as B lymphocytes and 32.7 ± 13.7% as macrophages. In terms of proliferation, the mean counts per minute were 4.3 × 10(3) and 1.8 × 10(4) for cells cultured in medium only or in the presence of concanavalin A, respectively, showing that CMC are viable and capable of responding to mitogen stimulation. Isolation of CMC and the subsequent phenotypic analysis of the different subpopulations were repeatable, with agreement indices varying between 0.5 and 1.0. Agreement indices for the proliferation assay were estimated at 0.8.

Immune cell differentiation in mammary gland tissues and milk of cows chronically infected with Staphylococcus aureus

This study identifies and compares the distribution of mononuclear cells in the mammary gland tissues and milk of healthy and chronically infected with Staphylococcus aureus cows. Somatic cell counts (SCCs) during the 3 months before the study were > 1 x 10(6) cell/ml in the infected quarters and < 1 x 10(5) cell/ml in the infection-free quarters. Immediately after slaughter, samples from the tissues above the gland cistern and supra-mammary lymph node were collected. No histological differences were found between the supra-mammary lymph nodes of the healthy and infected udders, and both appeared normal. In the milk of the healthy infection-free mammary glands, SCC was < 50,000 cells/ml) while epithelial cells were the predominant type. The percentage of CD18+ was low than 45%, of which over three-quarters were polymorphonuclear (PMN), and less than one- quarter were mononuclear cells. The later comprised CD4+ or CD8+ T-lymphocytes, macrophages (Mo) but not B-cells. In the tissues, there were few CD18+ leukocytes, and most of the cells were T-lymphocytes. The number of B-lymphocytes bearing CD21+ was similar to that of CD8+ and were localized in the connective tissue as clusters of 2-5 cells, mainly in areas with no alveoli, or as single cell having a dendritic like form. The number of Mos was negligible. In the milk of the infected glands, SCC exceeded 700,000 cells/ml, of which > 95% were CD18+ positive. The distribution of the leukocytes had two patterns: one presented (> 80%) of PMN cells and a small number of mononuclear cells; the second had less than 50% PMN and many mononuclear cells. The CD8+ cells in these infected sections were observed throughout the mammary epithelial cells (MEc) around the alveoli and in the alveolar lumen (AL). The numbers and the location of CD21+ B-lymphocytes were similar to those in the infection-free mammary glands. The number of CD5+ positive cells was lower than T and B- cells combined and were located throughout the mammary epithelial cells, around the alveoli and within the connective tissue. Mo numbers were high in most of those infected quarters, and were localized around the connective tissue and within the AL.

Lactation stage-dependent changes of lymphocyte subpopulations in mammary secretions: inversion of CD4+/CD8+ T cell ratios at parturition

PROBLEM

Determination of lactation stage-dependent changes in levels of lymphocyte subpopulations in milk.

METHOD

Flow cytometric assay was used to identify and assay lymphocyte subpopulations in bovine milk at different stages of lactation.

RESULTS

Lymphocyte subpopulations in mammary secretions of dairy cows change during the lactation cycle. In involuting glands (dry gland), approximately 80-90% of lymphocytes were CD2+ T cells. The proportion of CD2+ T cells, however, decreased to approximately 50% at the colostral stage an fluctuated between 50 to 60% in normal (mature) milk. Throughout the lactation stages, less than 5% were B cells as identified by the monoclonal antibodies against CD21 and MHC class II antigens. Subset analysis showed, however, that the proportion of CD5+ T cells decreased from 90% in involuting gland secretions to 75% in colostrum (peripartum stage), and to approximately 40-50% in the normal (mature) milk, CD4+ T cells constituted between 45 to 55% of lymphocytes in the dry gland secretion but decreased drastically at parturition and maintained at the level below 20% throughout normal lactation. In contrast, the proportion of CD8+ T cells in the dry gland secretion was low, between 30 to 40%, but increased steadily, in an inversely-related manner with that of CD4+ T cells, to approximately 40-50% at parturition and maintained at approximately 30-40% during the normal lactation stage thereafter. Two-color immunofluorescence study revealed further that practically all of the CD8+ cells in dry gland secretions were CD2+, and approximately 40% of them were CD5-. Throughout the lactation cycle, WC1+ gamma delta T cells comprised only 2 to 5% of lymphocytes in mammary secretions.

CONCLUSIONS

T lymphocyte subpopulations change dynamically during stages of the lactation cycle. The selective migration of T lymphocyte subpopulations to and from the mammary gland, and their functional roles in the immune competence and regulation of the dam and sucklings remain to be elucidated.

Effect of whole Staphylococcus aureus and mode of immunization on bovine opsonizing antibodies to capsule

Exopolysaccharide capsule is a major virulence factor of Staphylococcus aureus because it inhibits neutrophil recognition of antibodies to highly antigenic S. aureus cell wall. To circumvent this inhibition, two modes of immunization were tested for ability to induce anticapsular opsonins. Cows were immunized at drying off and boosted on d 14 and 28 by injection of Smith diffuse S. aureus plus dextran sulfate in the area of the supramammary lymph node or intramammarily. In cows immunized in the area of the supramammary lymph node, IgG1 and IgG2 sera antibody titers to capsule increased and remained elevated to the end of the study, 120 d postcalving. The IgM titers increased during the dry period but declined to preimmunization levels at calving. Response of serum IgG1 and IgM to intramammary immunization was similar to that with supramammary lymph node immunization, but more delayed and lower in magnitude. Antibodies of all four isotypes, IgG1, IgG2, IgA, and IgM, increased in dry secretions following immunization via lymph node. In cows immunized in the lymph node, IgG1 antibodies remained elevated throughout the study, but IgG2 antibodies dropped to baseline 15 d postcalving. In cows immunized intramammarily, only IgA antibodies increased significantly in lacteal secretions and remained elevated throughout the study. Immunization of cows in the lymph node during the dry period enhanced the ability of dry secretions and colostrum to support phagocytosis.

Influence of recombinant bovine somatotropin (sometribove) on mononuclear cells during the nonlactating period

Recombinant bST was evaluated as a potential immunoenhancer of bovine peripheral blood and mammary gland mononuclear cells during the nonlactating period. Cows (n = 4 per group) were assigned to one of four treatments: 1) untreated, 2) treated with recombinant bST during lactation only, 3) treated with recombinant bST during the nonlactating period only, and 4) treated with recombinant bST during lactation and the nonlactating period. Recombinant bST treatment during the nonlactating period had no effect on proliferation of bovine blood or mammary gland mononuclear cells in response to stimulation by mitogens or allogeneic cells. Recombinant bST treatment during the nonlactating period enhanced interleukin-2 secretion by mononuclear cells isolated from cows treated also with recombinant bST during lactation. However, recombinant bST treatment during the nonlactating period had little effect on interleukin-2 secretion by mononuclear cells from cows not treated with recombinant bST during lactation. Results of this study suggest that recombinant bST alters effector functions rather than proliferation of bovine mononuclear cells.

Proliferative response of mammary gland mononuclear cells to recombinant bovine interleukin-2

Methods of augmenting bovine mononuclear cell responsiveness during physiological transitions of the udder may enhance resistance of the mammary gland to intramammary infections. Interleukin-2 is required for proliferation of T-lymphocytes and may contribute to B-lymphocyte proliferation. Recombinant bovine interleukin-2 (rBoIL-2) was evaluated as a potential immunoenhancer of bovine mammary gland mononuclear cells. Bovine mononuclear cells were isolated from five primiparous Holstein cows at 14-18 and 28-32 days of involution and at 7-13 days prior to parturition. Bovine blood and mammary gland mononuclear cells were highly responsive to rBoIL-2. Response of mammary gland mononuclear cells to rBoIL-2 was comparable with response of blood mononuclear cells. These data suggest that rBoIL-2 may be an effective immunoenhancer of bovine mononuclear cells during the non-lactating and prepartum periods.

Modulation of bovine mononuclear cell proliferation during physiological transitions of the mammary gland

Mammary secretions and blood were collected from five primiparous Holstein cows 14 d following cessation of milking and 14 d prior to parturition for preparation of serum and mammary secretion skim fractions. Mammary secretions and blood were collected from the same animals 15 to 18 d following cessation of milking and 2 to 13 d prior to parturition for isolation of mononuclear cells. Effects of serum on mammary gland mononuclear cell proliferation and skim fractions from mammary secretions on blood mononuclear cell proliferation were evaluated. Mononuclear cell proliferation was evaluated in a mitogen-induced lymphocyte proliferation assay and in a mixed leukocyte assay. Proliferative responses of blood and mammary gland mononuclear cells did not vary significantly between the two time periods evaluated. Mammary secretion skim fractions obtained at both time periods significantly suppressed blood mononuclear cell proliferation. In contrast, exogenous serum enhanced mammary gland mononuclear cell proliferation in response to mitogens and allogeneic cells. Ability to enhance in vitro proliferation of mammary mononuclear cells isolated during physiological transitions of the mammary gland may suggest the potential for enhancing mammary mononuclear cell proliferation in vivo to reduce incidence of new intramammary infections at times when the mammary gland is highly susceptible.

Effect of bovine skim milk and whey on monocyte function

Previous studies have documented the ability of bovine milk to inhibit lymphocyte proliferation in response to mitogens. It is not known whether inhibition of lymphocyte proliferation is mediated through the action of monocytes. To address this question, we examined the ability of bovine skim milk and whey to affect monocyte function with emphasis on expression of major histocompatibility class II antigens and production of interleukin-1 by monocytes. Data showed that expression of major histocompatibility complex class II molecules and production of interleukin-1 by monocytes were not altered when monocytes were cultured in the presence of bovine skim milk or whey. Thus, it is unlikely that the suppressive effect of milk on lymphocyte proliferation could be mediated through alterations in the expression of major histocompatibility class II molecules or in production of interleukin-1 by monocytes. The role of other monocyte antigens or secretory products, however, should also be evaluated.

Lymphocyte blastogenesis inhibition by milk whey as an indicator of mastitis

Sixty milk whey samples prepared from quarters of five cows with a history of mastitis were tested for their ability to inhibit DNA synthesis in mitogen-stimulated lymphocytes. The inhibitory activity was compared with milk SCC, electrical conductivity, pH, and the number of colony-forming bacteria in the milk. Milk whey contained factors that inhibited DNA synthesis in cultured lymphocytes. Inhibition of mitogen-induced DNA synthesis increased with the clinical severity of mastitis and with increased values of indirect indicators of mastitis. The increases in inhibition and electrical conductivity were delayed past the increases in SCC. Milk whey (10 microliters) from quarters with clinical mastitis and from quarters with SCC greater than 900,000 inhibited 96 to 100%, 84 to 100%, and 69 to 100% of DNA synthesis in 3-d cultures of lymphocytes stimulated with Concanavalin A, phytohemagglutinin P, and pokeweed mitogen, respectively. The numbers of colony-forming bacteria correlated least with the inhibitory activity.

An evaluation of the mononuclear cells derived from bovine mammary gland dry secretions using leukocyte antigen specific monoclonal antibodies, light scattering properties and non-specific esterase staining

The distribution of mononuclear cells isolated from the bovine mammary gland during the nonlactating (dry) period was examined using monoclonal antibodies against leukocyte cell surface antigens, cellular light scattering properties, and the presence of nonspecific esterase. Most of the mononuclear cells isolated during the dry period were lymphocytes. T cells predominated until about 1 week prior to parturition. During the week prior to calving, the percentage of B cells increased until it approximated T cells. The ratio of CD4:CD8 cells was 2-3:1 for mammary gland T cells. This was similar to the ratio found in peripheral blood. At dry-off, about 12% of mammary mononuclear cells were macrophages. The macrophage percentage increased (to about 30%) at mid-dry and remained at this levels until parturition. PMN's were isolated with the mononuclear cells during the first 2 weeks dry and the week prior to calving. Three methods were used to identify mammary macrophages. Esterase staining (as an enzymatic method), forward angle/90 degrees light scatter (based on size and internal complexity), and MHC class II/forward angle light scatter (based on size and surface markers) were compared. Each method yielded similar specificity for macrophage identification. Non-adherent cell fractions, obtained by passage of the cells over Sephadex G-10 columns, were enriched in CD4 positive T cells, somewhat depleted of B cells, and depleted of macrophages and PMN's. Cells eluted from G-10 columns, with lidocaine, were mostly lymphocytes, but reflected the cells loaded onto the column.

Culture conditions for blastogenic responses of bovine mammary mononuclear cells

Several experimental parameters were examined to determine optimal conditions for proliferative responses of mammary mononuclear cells (MMC) obtained from six nonlactating dairy cows. These parameters were: pre-incubation of cells in medium prior to assay, mitogen concentration, assay incubation time, and type of culture medium. Response variables included viability of cells and the rate of proliferation as assessed by tritiated thymidine incorporation. Pre-incubation of cells in medium had no effect on the proliferative response of MMC. Whereas Concanavalin A (ConA; 3.3 or 6.6 micrograms/ml) and phytohemagglutinin (PHA; 1, 5, 10 micrograms/ml) did stimulate proliferation of MMC, the higher doses did not stimulate greater proliferation than the lower doses of mitogens. The greatest mitogenic response was obtained on days 2 and 3 of incubation. Proliferative responses were significantly higher at all mitogen levels tested in a 50-50 mixture of Rosewell Park Memorial Institute medium 1640 and Liebovitz-15 medium (RPMI/L-15) than in RPMI alone. Viability of MMC was also significantly higher in the RPMI/L-15 medium. To test whether the significant effect of media on blastogenesis was specific for mononuclear cells from the bovine mammary gland, peripheral blood lymphocytes (PBL) from four dairy cows were cultured with ConA and PHA in a mitogen assay in both RPMI and RPMI/L-15. Viability was measured on day of collection and on all culture days. PBL were stimulated equally in both media. PBL viability decreased significantly on day 1 in both RPMI and RPMI/L-15. These results suggest that the optimal culture conditions for blastogenic responses of mammary mononuclear cells and peripheral blood lymphocytes may differ.

Ability of bovine mammary macrophages to enhance proliferation of autologous blood and mammary secretion lymphocytes

Cells were obtained by centrifuging the mammary secretion of healthy udders of 19 cows during the dry-period and during mid-lactation. The suspended cells were incubated in plastic wells. Those adhered cells classified as mammary macrophages were incubated with pokeweed mitogen (PWM). Autologous peripheral blood lymphocytes were added to wells containing untreated macrophage cultures or cultures pretreated with PWM. In seven cows autologous dry-period mammary lymphocytes were added instead of blood lymphocytes. The macrophages + lymphocyte cultures were subjected to the lymphocyte stimulation test (LST). For comparison, peripheral blood lymphocytes and dry-period secretion lymphocytes were also subjected to the LST in the presence of PWM. In all cases, mitogenic responses were higher in pretreated macrophage cultures than in background control cultures. The stimulation indices (SI) showed that PWM-pretreated dry-period mammary macrophages enhanced the proliferation of autologous peripheral blood lymphocytes to a greater extent than did blood lymphocytes plus PWM (49 +/- 10 v. 30 +/- 6; P less than or equal to 0.05). Mammary macrophages taken from the same cows but during midlactation also clearly induced proliferation of autologous peripheral blood lymphocytes but to a lesser extent than dry-period macrophages (16 +/- 2 v. 49 +/- 10; 16 +/- 2 v. 30 +/- 6; P less than or equal to 0.01 and P less than or equal to 0.05). The PWM pretreatment of mammary macrophages increased the proliferation of autologous dry-period mammary lymphocytes by at least a factor of three (28 +/- 8 v. 8 +/- 2 P less than or equal to 0.05). The present results indicate that bovine mammary macrophages pretreated with PWM enhance proliferation as well as modulation of mammary and peripheral blood lymphocytes. The modulation of lymphocyte stimulation as demonstrated here in vitro, has great significance regarding aspects of local immunostimulation related to modern treatment of mastitis.

Alterations in neutrophil phagocytosis and lymphocyte blastogenesis in dairy cows around parturition

The bovine blood neutrophil phagocytosis and the blood and milk lymphocyte proliferative response upon stimulation with Phytohaemagglutinin, Concanavalin A and Pokeweed mitogens was studied from 3 weeks prior to calving until 3 weeks after calving. Neutrophil phagocytosis and the total and differential blood leukocyte counts were performed by flow cytometry. A gradual increase in the percentage of phagocytized bacteria and the average number of bacteria per phagocyte was observed before calving followed by a sharp fall on the first postpartum. This was followed by a steady increase in the above parameters reaching the highest levels at two weeks postpartum. There was a gradual increase in the number of neutrophils in blood as calving approached followed by a sharp decrease after calving. The number of lymphocytes in blood dropped before calving, being at the lowest level on the day before calving. The proliferative response of blood and milk lymphocytes upon stimulation with the three mitogens was low during the week preceding parturition with the lowest value on the day before calving. The response of blood lymphocytes returned to a higher level the second week after calving while that of milk lymphocytes remained at a low level during the first and the second postpartum weeks.

Immunological aspects of mammary involution

Frequency of new intramammary infection is greatest during early involution, decreases during middle stages, and then increases prepartum. Penetrability of the teat canal, antibacterial properties of keratin, bacterial adherence, and epithelial sensitivity to toxins play a role in resistance. Leukocytes phagocytose bacteria and regulate expression of immune mechanisms, although their function is compromised during certain stages of involution. These cells increase to millions per milliliter as involution progresses and then decrease prepartum. Macrophages predominate in lacteal secretions, followed by lymphocytes and neutrophils. Lactoferrin, a major whey protein and iron chelator, is also associated with resistance to infection during the nonlactating period and may have immunomodulatory properties. Lacteal immunoglobulins increase throughout involution peaking prepartum and function by opsonizing bacteria, neutralizing toxins, and preventing bacterial adherence. Immunoglobulins are derived from blood or are produced locally by plasma cells present in the subepithelial mammary stroma. Plasma cells, lymphoid cells, and other protective leukocytes present in teat end tissues accumulate during infection and concentrations increase in response to local antigenic stimulation. Various aspects of the mammary immune system are compromised during periods of functional transition. Thus, vaccination, immunostimulation, accelerated involution, and intramammary devices are some methods now being tested to amplify local immunity and protect the gland from bacterial infection.

Approaches to the manipulation of mammary involution

Mammary involution is a gradual process that occurs following cessation of milking. Regression of mammary secretory tissue accompanies dramatic changes in secretion composition during the transition from lactation to involution. Conversely, rapid differentiation of secretory tissue and copious accumulation of colostrum occur as parturition approaches. The duration of the nonlactating period, mammary gland health, and secretory cell response to hormones influence subsequent lactational performance in most species. Manipulation of the bovine mammary gland in an attempt to hasten involution has been studied. The primary objective of these studies was to determine if hastened involution would decrease new intramammary infections during the early nonlactating period. Results of these studies have also led to a more fundamental understanding of events that occur during physiological transition of the mammary gland. Adequate regression, proliferation, and differentiation of mammary secretory epithelium during the nonlactating period of ruminants appear to be essential for maximal milk production during lactation. Factors that interfere with these mechanisms can adversely affect mammary function during the impending lactation. A greater understanding of these processes may provide new approaches for increasing milk production in dairy cattle.

Inhibition of bovine peripheral blood mononuclear cell blastogenesis by fractionated mammary secretion

1. Bovine mammary secretion whey obtained during late involution markedly inhibited mitogen-induced blood mononuclear cell blastogenesis. 2. Whey proteins eluting in the first and second absorbance peaks following molecular exclusion chromatography were associated with greatest inhibition of mononuclear cell blastogenesis. 3. Greatest inhibition of concanavalin A-stimulated mononuclear cell blastogenesis was associated with high concentrations of whey proteins in absorbance peak 1. 4. Whole mammary secretion whey and whey proteins in absorbance peak 2 caused similar inhibition of concanavalin A- and phytohaemagglutinin-treated mononuclear cells. 5. Differential inhibition of mitogen-induced blastogenesis may reflect the presence of immunosuppressive substances in bovine mammary secretion whey which differ in specificity for bovine T-cell subsets.

Distribution of T and B lymphocytes in mammary dry secretions, colostrum and blood of adult dairy cattle

The distribution of lymphocyte subpopulations from dry secretions, colostrum and blood from 10 healthy adult Hostein-Fresian cows was studied using the TH21A and B26A mouse monoclonal antibodies (MAb) to adult bovine B and T lymphocytes, respectively. The mammary gland lymphocytes (MGL) were isolated from composite sample of all four quarters by density centrifugation over discontinuous gradient of ficoll-diatrizoate. The peripheral blood lymphocytes (PBL) were purified using the ficoll-thrombin method. Isolated PBL and MGL were analyzed using the two fluorochromes method (TFM) and laser flow cytometry (LFC). The mean viability of isolated PBL and MGL from dry secretions and colostrum after the TFM and LFC were 92.4% +/- 3.2%, 91.4% +/- 6.0% and 87.1% +/- 6.1%, respectively. There was a good correlation between the two MAbs and the percentage of surface immunoglobulin (SIg) positive cells in the peripheral blood using the TFM. The PBL yielded a mean percentage of 21.2% B cells, 66.4% T cells and 9.4% "Null cells" (TH21A+; SIg-). The TFM on MGL from dry secretions and colostrum indicated two distinct patterns (group I and II) of SIg and reactivity to MAb markers (p less than 0.001). The MGL data included in group I and group II were gathered from both colostral and dry secretions. In comparison to the distribution of lymphocyte subsets within peripheral blood the mean percentages of B cells, T cells and "Null cells" in the mammary gland were respectively, 2.8%, 88.1% and 5.4% for group I and 3.5%, 89.0% and 15.1% for group II. In the mammary secretions, the use of SIg alone was not considered to be a good marker for B cells; in four animals a mean percentage of 15.6% (13.9/89.0 X 100) of the mammary gland T lymphocytes were also SIg+. Of the TH21A+ MGL, only 18.8% were SIg+ in group II compared with 34.1% for MGL from group I and 69.3% for the PBL. Marked differences in cell size distribution and cell surface antigen density were found when PBL and MGL from dry secretions were compared by LFC using the B26A MAb. The results of this study demonstrate a difference in the percentages of peripheral blood and mammary gland B and T lymphocytes and confirm previous findings in which the T lymphocytes were found to represent the major subpopulation of lymphocytes in bovine mammary secretions. This may represent an essential event in the adoptive transfer of cellular immunity through the colostrum in cattle.

Management of dry cows to reduce mastitis

The objective of mastitis control during the dry period is to have as few infected quarters as possible at calving. This depends on enhancing elimination of infections present at drying off and on reducing the new infection rate during the dry period; prevention of new infection appears to offer greater long-term benefits. Incidence of new infection is high in the dry period with periods of high susceptibility shortly after dry off and again prepartum. Pathogens of both contagious and environmental origin cause new dry period infections; however, exposure to contagious pathogens probably decreases with cessation of regular milking, whereas exposure to environmental pathogens continues throughout the dry period. Varying susceptibility over the dry period may be affected by bacterial loads on the teat skin, characteristics of the teat canal, and internal protective mechanisms. At present, antibiotic therapy at the end of lactation is the most effective means of eliminating existing infections and preventing new infections. Although there are reasons to prefer selective therapy, present evidence favors a recommendation for treatment of all cows at the time of drying off. A shortcoming of present therapy regimens for the dry period is that they provide little or no protective effect against new infection prepartum. Other mastitis control methods and management practices have not been shown conclusively to reduce new dry period infections. However, it appears that reduction of exposure to environmental pathogens during dry period should be recommended. More effective means to reduce new infections in the prepartum period are needed.

Effect of chronic staphylococcal mastitis on mitogenic responses of bovine lymphocytes

We compared mitogenic responses of milk and peripheral blood lymphocytes from nonmastitic (control) cows and cows with experimentally induced staphylococcal mastitis in one gland. Milk lymphocytes from infected glands were essentially unresponsive to Concanavalin A, phytohemagglutinin-P, and pokeweed mitogen. Proliferative responses of milk lymphocytes from uninfected glands of infected cows were not as depressed as those from infected glands but were significantly less than those of milk lymphocytes from control cows. Proliferative responses of peripheral blood lymphocytes from control and infected cows to Concanavalin A and phytohemagglutinin-P were similar; however, peripheral blood lymphocytes from infected cows responded in reduced fashion to pokeweed mitogen compared with peripheral blood lymphocytes from control animals. These observations demonstrate that in vitro lymphocyte blastogenesis is markedly depressed during infection, suggesting that in vivo lymphocyte function is compromised, possibly contributing to the chronicity of staphylococcal mastitis.

The immunophysiological basis for vaccinating ruminants against mastitis

The roles of humoral and cellular defence mechanisms in protection of the mammary gland against bacterial infection are reviewed. Effective protection depends on opsonisation of pathogens and subsequent phagocytosis by neutrophils. A concomitant requirement for protection is the rapid infiltration of neutrophils into the infected gland. Immunological studies have shown the need to prime animals against antigens expressed by bacteria when they grow in vivo. Vaccination procedures which promote these mammary defence mechanisms are discussed.

Depression of B-lymphocytes by mastitis and treatment with levamisole

Proportion of B-lymphocytes in milk and blood decreased simultaneously with development of mastitis induced with endotoxin and recovered with disappearance of clinical signs. However, the change in T-lymphocytes was slight. The reduced percentage of B-lymphocytes was caused by reduction in absolute number of such cells. When used orally, levamisole increased the proportion B-lymphocytes of milk to the same as or more than that of similar cells in peripheral blood. This compound may enhance activity of the bovine mammary immune system and be of value for control of bovine mastitis.